I can only speak for myself obviously but I'm totally tracking with your question. I very often ask myself the same thing, and at the same time ask myself if it is an attitude that I aquired as I got older.
I remember that in my 20's I was all into the skinny woman with big boobs thing. Was I buying into the Madison Ave ideal of the perfect mate? Probably, after being hit in the face by adds for colas, chewing gum, cars and shake and bake.
I haven't posted much here so no one knows this yet, but I'm really heavy into what I call my "caveman point-of-view". I've read several books in my life that dealt with our very early ancestors, and as a result I often take a look at a situation as a caveman, or cavewoman would. This might sound odd or funny, but I find that it cuts away a lot of the often irrelevant crap that surrounds our lives. Also, as a result I am constantly thinking of the effect that our own genetics might have on our behavior. I think that we very often behave in ways that we do because as early human beings we had to develop a behavior that would facilitate survival. Having said all that:
I think that when we, as men and women, consider other men and women, one of the things that takes place, mostly in the subconcious, is we consider their status as a possible mate. One of the factors involved in this process, in my opinion, is we evaluate the health of that possible mate. Now enters Madison Ave through all the media that assaults our senses everyday, and tells us that the "healthy" mate has a skinny body, blue eyes, blond hair and huge boobs if you're a guy, and a big hot car, smooth chin, no grey hair and a sixpack (abs) if you're a woman. I could go on with this, but I'll spare everyone...
All I know is that somewhere along the line I learned that a woman has substance, that a woman is more than flesh and bones and giggles. Somewhere, some how, I learned that a woman is inside her brain first, then in her body. Then... low and behold, I discovered - around the same time that I started to find "girls" uninteresting - that a woman with some meat on her bones is more fun because they are the ones who tend to have the interesting brains.
Of course to everything there is an exception and I can accept that because I'm a laid back kinda guy.
Hope I didn't bore anyone.
wg