Aww, thanks, bb!
I agree. He must have been thinking he shouldn't take a chance on pissing Sam off right now. Perhaps sense dthat doing something so brotherly would not be welcome by Sam, and could enc in a lot of heartacje for Dean, just for the rejection in Sam's face. Ties into the "I know, you wouldn't have done the same for me", which is perhaps the most crushed thing I've heard from Dean in ages.