I'm gonna be honest and say the blunt truth about this, but whenever you buy a Nintendo consoles, it's almost default to have those games as points for an argument case. Every one who buys a Wii U, know what to expect. You're going to get the same obvious Nintendo titles and therefore, have a reason to come back to it, whether there is third party support or not.
Yes, but as we've seen with Wii U, just because these games are always there doesn't mean that they will sell as well as or better than they did in the past.
Meanwhile, in the "core games" category, Wii saw some the best-selling games Nintendo has had since NES. On Wii:
NSMBWii sold better than any console Mario game since SMB in 1985
Galaxy sold better than any 3D Mario game period
MK Wii sold more than all the previous console entries combined
DKCR managed to sell better than every game since the first
SSBB outsold SSBM by about 4m
TP is the best-selling Zelda game since OoT (and tops it if you count GCN sales)
But on Wii U:
NSMBU sold worse than any console Mario game
SM3DW then proceeded to sell even worse
MK8 is not tracking well compared to past MK games
DKC:TF has sold less than 1m WW (as of June)
SSB4 and Zelda are obviously pending.
Why are the core Wii software sales a point in Wii's favor? Because those sales show that Wii attracted
more gamers to Nintendo's "core games" than past Nintendo consoles.
The data seems to suggest that Wii managed to retain a large number of N64/GameCube era customers (with N64/GameCube sequels) while at the same time attracting new gamers (with motion games) and lapsed customers (with retro-style games). Even if you want to argue that they
didn't retain a large number of customers, they were certainly doing a capable job of replacing those customers with new customers.
And it's no surprise, really.
NSMBWii was the answer to the 2D Mario drought that had been ongoing on consoles for about 15 years. It was a new 2D Mario that even if it wasn't terribly ground-breaking at least did a good job of showcasing tech advancements since SNES (with simultaneous multiplayer, its clean 2.5D visuals, etc.).
Galaxy was a course-correction from the overly-un-Mario direction of Sunshine back to the old SM64 feel... oh, and with the added curveball of gravity to make you feel like you're playing your very first 3D platformer all over again. The art direction was really stellar and they did a good job flexing Wii's muscle, too.
While MKDS was a dev-declared effort to make the best MK game since the first, MKWii was an effort to make the best MK game possible using Wii technology. Clearly they did a pretty good job at bridging the "best possible MK" and "accessible to new audiences" concepts in one game, even if some of the mechanical changes didn't stick. TBH I have very little insight into how this game was received when it was announced/launched since I was in a weird transition period at the time.
DKCR followed a similar template to NSMBWii, and had similar success, although obviously scaled to DKC-level proportions. Not much else to discuss here.
Before SSBB launched, there was a very well-coordinated hype campaign that really pushed home the character roster and the Final Smashes. Obviously in hindsight the game was seen as unnecessarily messy and cluttered (hence the prevalent Melee renaissance), but there was a lot of energy behind its launch. And as a mascot-heavy game Smash Bros. is hardly a poster child for "games that sell to people who are new to gaming." (It will sell to children, but not to older non-traditional gamers.)
I don't think the reception of Twilight Princess needs to be thoroughly discussed, either. That game was on fire even before it was slated for Wii. It was a great tease during the final years of the GameCube that had everybody excited about Nintendo, which was great fuel for the Wii launch fire.
That said, the Wii end-of-life and Wii U transition is a pretty good case study for how
not to retain customers.
Remember how most of Nintendo's biggest games from the GameCube era were front-liners for the Wii launch period? That's because those were Nintendo's "core games" - and by that I don't just mean their games for "core fans," mind you, but "core games" as in "their biggest source of revenue." With Wii, their biggest source of revenue - their new "core games" - were new market games like Wii Sports and Wii Fit.
But Nintendo basically abandoned new market games after 2009, with the release of Wii Sports Resort and Wii Fit. They seem to have thought that Just Dance was enough to keep the momentum going in the meantime. And at the Wii U launch, the only real first-party answer for the new market was Nintendo Land--a game that is covered with Nintendo franchise branding and thus incredibly unaccessible to anyone who is not familiar with those franchises (from a marketing perspective, the exact opposite of Wii Sports, which used no pre-established brand image).
Is it any surprise that the new market didn't return for Wii U? Nintendo basically stopped selling to them in 2009. If you asked Nintendo, they would probably say that they
did have games for this audience that debuted after 2009--they were games like Metroid: Other M and Skyward Sword. But obviously these were such failed compromises that they did a poor job of attracting both their traditional audiences as well as the new market. And unlike Twilight Princess, which got lots of people pumped about Nintendo going into 2006, these games actually generated brand friction which brought any excitement about Nintendo to a halt.
NSMBU and SM3DW, while both fun and polished games, are token efforts at best, and the market has definitely reacted to them as such. NSMBU has refined level design compared to its predecessors, but does very little to really show off the hardware differentiation between Wii and Wii U; SM3DW likewise was not positioned to be a show-stopper like Galaxy was, which is a death sentence for a 3D Mario game.
DKCTF is a great game and a good follow-up to DKCR, but only to the same extent that DKC2 was a good follow up to the original DKC. Gating it off on a more-expensive platform three years later (remember, DKC was an annual franchise on SNES) was not the best way to satisfy DKCR fans.
MK8 seems to be doing OK (as it should; it borrows a little heavily from MKWii and 7 but otherwise rises above a lot of the trappings I just described), but it's not going to turn Wii U around by itself.
Instead of debuting Wii U with the next Twilight Princess, Nintendo released an HD remake of TWW, citing the poor GameCube sales as the reason for its low popularity and declaring that Wii U will give it a new audience. Do the sales suggest that TWW is more accepted today than it was during the GameCube era? I don't think so. Despite being part of a premium bundle, TWW HD did very little to drive Wii U sales.
The new Zelda game looks great (to me personally), but it seems like they've grabbed the NPC shaders and lighting engine right out of TWW HD. I don't think it's going to fit in alongside modern expectations for how fantasy should look--which is not to say it should look like Skyrim (maybe more like TP's LotR-esque style), but that today's "all-ages" fantasy adventures like Tangled/Frozen have a better (read: more appealing) art direction that it doesn't even try to match (much less surpass).
Wii's software was all incredibly relevant and exactly what it needed to be given the time, place, and market conditions. Wii U's software, on the other hand, has (at least so far) been exactly the opposite.
tl;dr - Just because the software lineup has familiar names doesn't mean that expectations of Nintendo haven't changed. Wii represented a time when expectations were at an all-time high, such that Nintendo was both retaining lots of old customers and reigning in
lots of new customers. But Nintendo hasn't really done a good job on either front with Wii U.