"Good" is in the eye of the beholder.
Speaking as someone who has had years of experience in PC games and who has jumped into the iPad world with both feet, my observation is that iPad games often have some attributes that tend to make them better than PC games, although of course for any given game there's no guarantee.
(1) The limited input modalities mean that the UI has to be good for the app to be good. There's no nonsense like "Press G to throw a grenade, but B for a Satchel charge and S for a molotov cocktail" (yes, Commandos, i AM looking at you.) Again, there's obviously no guarantee but developers who want to release a quality product are sort of FORCED to polish the UI. And that's a good thing.
(2) Having the game with you everywhere is completely life-changing.
(3) Having multiplayer turn-based games with you everywhere is completely life-changing. If I'm waiting at the car dealer, and they have wi-fi, I can play a move in my chess game, or a round of Battle Academy, or - soon - Combat Mission. I don't have to wait until I get home. This. Is. Freaking. Huge.
(4) If the game has Gamecenter integration, then the way you find opponents for online play goes from "Somewhat annoying bespoke thing where I have to track individual passwords for each publisher" to "touch this button and you're playing."
(5) Generally speaking, the graphics on the platform are way better than you would expect them to be.
None of this is to say that all iPad games are better than all PC games. But the platform has some real strengths, and I think we're beginning to see developers start to exploit those strengths.
In other words, while a game isn't better just because it's on the iPad I don't think it's a given that PC games are by definition 'better' either.