Why do women display cleavage?

Yesterday’s Dear Abby had a letter from a man wondering if it is rude or not to occasionally look at a woman’s breasts when talking to her. Of course Abby said it is very rude (I agree) and that is why some women say “hey, I’m up here”.

But it made me wonder, why do women complain about men checking out their boobs, yet wear low cut tops that accentuate their breasts?