I'm not suggesting that people won't eventually come back to it. I'm just saying: all games made today follow a basic formula, tuned to various levels of complexity, violence, and the little things we call genres. There's a niche that's fed by the most complex expression of that formula. What people are noticing now is that the formula is limiting them - or that, among the games produced by the formula, the only ones that break out of the niche are the ones that are about as simple as it gets.
What I'm suggesting is that every publisher, smelling where the money's at, will swing either to the simple side of the 10%, or throw their whole weight behind the 90%. When it takes ten, twenty, fifty million dollars to make a big game (and a complex game is a big one), why would a publisher even bother making one if they don't have ten million people ready to buy it? It's possible for a complex game to make its money back in its little niche, but why try it when there are bigger fish to fry out in the mainstream?
The thing you're getting at is that eventually, they'll run out of bigger fish, right? I completely agree. But 90% of the population is a lot of people. How long will it take for the game industry to diversify enough to the point that these 90% start to recognize which if the Popcap-style fare is worth their dollar, and become discriminating consumers? From the moment the market opens up until they spend about as much time picking their games as they do, for example, their television, then they'll be a market who'll buy just about anything if it's casual. In this environment, game companies will have very few reasons to make the same-old same-old, and they wouldn't make one that very deliberately does not appeal to anyone but fans of the same-old same-old. The effects will be exaggerated because publishers imitate and they have to predict things years in advance.
My concern is that it will take so long for a nuanced market to spring up that publishers will, during that time, adopt an entirely new formula, that doesn't account for the production of big complex games. A game like that can only be made reliably in two circumstances: a market that is fundamentally limited to that niche, and a market that is very nearly as diverse and democratic as books or music. There's a long way between those two states.
Things like this have happened to other media and even entirely different kinds of product. When was the last time you saw, for example, a feature-length satirical comedy in the vein of Duck Soup? How often do musicals get put on the big screen? How about a TV show that couldn't be pigeonholed into "sitcom," "drama," "documentary," or "reality?" An unapologetic, serious, pulp comic without superheroes in it? A car that isn't shaped like every other car, either in the interior or the exterior? You get a few novelties here and there - but it is possible for the little niches of consumer goods to be forgotten when the product as a whole goes mainstream.
The Internet is mitigating all of this to varying degrees, usually inversely proportional to the budget required. I'm hoping that's enough to keep it from happening to games, but I'm not convinced it will be.