That certainly will have some influence on the images. But not enough to explain the differences. Mostly, yes. It's too bad that your friend's images don't come with the EXIF data - they would provide a clue as to how far your friend's and your exposures differ. But I am fairly certain that something quite similar to your friend's image can be pulled out of your RAW files as well (despite me being unfamiliar with exactly how much processing Canon RAW files can endure before falling apart). Why don't you ask your friend how exactly the images were processed? Or better yet, have him show you on yours?