I think it is a societal thing. There was recently a story in the NY Times about what guys do when they go out together, and it pretty much says straight guys do not do things like go to a really fancy restaurant, or to a museum together because, of all things, many of them fear that someone will see them together and assume they are gay.

It is slowly changing, however. In my generation I remember many fathers whou would not hug or kiss their sons...which is pure insanity. I also note that a lot of guys now greet each other with a hug, something that is done in Latin countries world wide. Guys are also much more prone to cry in public than they used to be.

As for some things, like noticing shoes, or going "shopping" for hours on end without buying anything, I think we are wired a bit differently. I think this is why guys sometimes get into trouble with the women in their lives by failing to notice a new hair do or new shoes etc.