Sure, demographics have something to do with it, but if you think that something as small as missing DLC cars doesn't factor in then that's no different than ignoring the demographics issue. I used to work in a game store and small things like this were enough to sway people into buying a different version. Why buy an incomplete version of the game? Is it small? Yeah, but just the other day I had someone tell me that's why he didn't buy the Wii U version. He wanted the cars and picked it up on the 360 at the local game store here in Japan.
Still, that also doesn't account for the Nintendo versions of the game being gimped in some way or just plain late to the party by a few months.
Doesn't explain why when things like the Sonic Racing game that launched had glitches that need to be patched, yet sold well for Wii U. Or Just Dance 4 was a crappy shameless Wii port. Or this LEGO City game had atrocious load times and sold well, comparatively. Your argument for a super informed userbase that rejects games for technical merits falls apart when you look at some of the game that have sold much better.
You may have worked at a game store, but I've worked at a retail store throughout all the holidays and the types of people that buy this stuff. I've been asked a dozen times on the demo Wii U unit what it was, is it the same as the Wii, does it come with all the games IN the demo unit, or so on. The few people that I've actually sold a Wii U too, or Wii U games too, lets just say aren't a bastion of technical knowledge.
I've sold about 100 times more copies of budget Dora's plaything or Monster High dress designer shovelware for Nintendo systems than I can count. Meanwhile when people come in for a 360 or PS3 game, it's always the same thing. Call of Duty. Halo. Madden. Far Cry. Whatever else.
Safe to say, I've got a pretty good idea who is buying what over probably a few hundred transactions doing this stuff. What you see on the internet and what we're talking about right now is not something the general Nintendo console owner is even aware of. It's a family and budget conscious ecosystem.
