Here's how much of a man-child I am: I see "The Jiggly Problem" and think of Jigglypuff.
But you're right, somewhat, there is a curiosity surrounding the big mounds of flesh and fat on the chest of a woman.
I recall a time when I was but a mere freshman in high school. I'm walking down the hall one day, when I'm suddenly blind-sided by a well-endowed pair. Emphasis on the "blind." This particular pair was half-exposed, covered in glitter, and moved with just a bit of jiggle.
It's scientifically proven that the three things that most attract any person's gaze are: large objects, shiny objects, and moving objects. The pair in question exhibited all three properties.
ANYWAY, I notice the pair, because I couldn't not notice. She noticed that I noticed, and gave me a face. Gentlemen, I think we all know that a face can be just as insulting and infuriating as someone saying something, often even moreso. All I said was, "You have shiny shit on your cleavage. Why would you do that if you didn't want people to look?" Then I walked away very quickly, as I was deathly afraid that she would throw a hissy-fit.
Okay, that's only half-true. I noticed the pair, which was indeed large, exposed, and glittery. She didn't notice me noticing, but it really got me thinking about the thought process of, "I'm going to show off my boobs, but I don't want guys to really look at them," that a disconcerting number of ladies seem to have.
Now, with all that said: Why would women be alright with guys noticing legs, but getting all in a tizzy when we notice the breasts? Well, I almost had an explanation, but then I realized it was kinda dumb. I'll be honest, I've got nothing for this one.