I don't like playing games on the PC, it's never been something that appealed to me. It's not the PC itself, but rather the controls. If I can plug in a controller, like I did with my xbox controller when I played ffxi briefly on PC, then I'm up for it, but I'd plump for a console due to being able to play on my 42" TV.
The achievement/trophy thing may seem irrelevant, but it's not. I can't speak for PS3 (though the general idea is the same), but achievements are a major part of my game-playing. If I like a game, I'll play it, but I'll always look at the achievement criteria and see what I can work towards - I guess it helps develop a sense of achievement, or for a better word, accomplishment. Especially nowadays, completing a game isn't just completing a game. You can complete it several times, not just on different difficulties, but choosing different paths, or completing the game the fastest way you can VS. taking your time and finding collectables etc.
Achievements are a major part of my gaming experience, but0 even if PC were to add some form of achievement idea, I'd still stick with console. I play on 360 just now, but only because it was cheaper than the PS3 when I got it and the games were better. When this Xbox breaks, which it will, I'll assess the games out at the time and in the foreseeable future and see which one tickles my fance. PC is very much in last place in terms of what I'd like to play games on... well ok, it's just above the Wii.