Fewer PC games are, as a general thing, being made. Now, go wade through Newground's or Kongregate's games and you'll find where all those game developers have dissapeared to.
Saying that the average quality of PC games has improved is like saying that, because you've slaughtered all your sickly cows, the average quality of your cows has improved. It might be true, but it doesn't mean your healthy cows are any better off. The only reason the "quality" of games has improved is because they're made by companies focusing on putting out cheap rip offs with marginally better graphics year by year. Essentially, nothing new is being made (not truly, anyway) only the old is being recycled.
There are no small developers left, really, and the big ones have become clone factories. I can put up with bugs etc if there's a good game underneath it all. I think Dungeon Keeper was rated from like 70% to 90%, and Dungeon Keeper 2 similarly, but they were excellent games looking back. And that was for control troubles etc, which I think any real gamer could put up with to get to the game underneath. Look at, in contrast, Dragon Age Origins. That game left me yawning about two hours in, as I could already tell how everything was going to happen in it and there was very little pulling me in. Yet, that got scores in the 9/10s and high 90s. Why?! It'd been done before, the graphics weren't particularly amazing, the story wasn't anything new, the controls could be quite awkward, the gameplay wasn't balanced etc etc. Why did it get such high scores?!
The same with Mass Effect, except that game's controls were even worse.