I don't think it's as simple as "make good games," though.
I think Michael is right that branding matters. I've put it a different way in the past: I've labelled them Umbrella Games. This refers to the biggest games available, which give shade to the smaller, less well known efforts to grow and prosper. I believe virtually all hardware is moved on the backs of the top 10% of games. The big hits are what motivate people to pay attention to or purchase a specific system, and then they stay for the mid range fare. A great example of this in the past is GTAIII. I think that moved enormous amounts of hardware. FFXIII just produced what was by far the biggest hardware week in the PS3's history in Japan. The announcement of DQIX for the DS produced an explosion of succesful JRPGs for the system in Japan. There are many examples of this. These major, well known games attract users who go on to buy less well known games in the same genre.
In some cases, those smaller games are very good (Infamous seems to be well liked, as a Sandbox game, and Tales of Vesperia got similar reviews to FFXIII), but I believe these games would absolutely flounder without the big games to establish the base there.
Well, the big games in the casual arena are indeed on the Wii. Those games are made by Nintendo themselves: Wii Sports, Wii Fit, Brain Age, and so forth. And so casual fare has done fairly well on their systems -- certainly much better than they've done on the PS3 or 360. But the hardcore umbrella games are almost all made by third parties, and almost all of them were made for the PS3/360. In fact, most were already headed to the PS3/360 before this generation even began (GTAIV, Assassin's Creed, Final Fantasy XIII, Metal Gear Solid 4, etc. etc.)
So the "Umbrellas," or Brands, as Mr. Pachter calls them, are all established on the PS3/360 now, in regards to the hardcore. I don't think it would be as simple as making good games now: you'd have to make huge, gigantic games for the Wii, to try establish the base there. If that were to happen, then smaller but still very good games can start doing well.
But I don't see much incentive to do that. You'd not only have to convince these purchasers to buy a Wii, you'd have to convince them to buy a Wii instead of a PS3/360, which is where third parties have largely been directing consumers since the generation began. That's a tall order, and would likely be prohibitively expensive. It's not worth trying, in other words.