Uh, yeah. Why can't you? I can touch type on my iPad just like any other system.
The only person that "can't" something is you. And that "can't" is, apparently, have the creativity to envision a system that MOVES THE CONTROLS to be under your fingers instead of the other way around. iOS games already do this.
It shouldn't matter where my fingers go. I can have ten commands right in front of me at all times! Sixteen, actually. They should just always be there.
I think you're missing what he's saying, i consider myself an extremely good gamer and i cannot utilize a touchscreen for controls without looking at the screen because there is no feedback to let you what you're touching. Basic controls are easy where the movement is on the left side of the screen and there is maybe one or two buttons on the right edge, start adding in more buttons and you see the real problem.
I've Airplayed Vice City from my iPad and it was horrific, it was impossible to look solely at the TV and hit the controls EVERY TIME. It made the game terrible to play and quite simply just frustrating that i quit and went back to just playing it on my ipad. Even with Final Fantasy 3, exploring the game is fine but when it comes to battles its a pain in the ass to play as its hard to always select what you want in battle if you're looking only at the TV. These control issues make the game a problem that shouldnt exist (its a problem when airplaying) and is why you need physical buttons to hit a wide array of games that can be more complex and intuitive than what solely a touchscreen can offer.