Tbh, I probably should have only got the 360 version, especially considering the improvement in graphics this time around.
However I did the same with Dragon Age Origins. I bought PS3 & PC versions.
So I can play it with 'better' graphics and on my laptop when I'm away. (Trust me a week in hospital a week or so ago, made me appreciate being able to game via bootcamp too).
Ah, ok. Fair enough.