Context note: the wu below answered questions in a now deceased write-up: why are women so concerned with their weight? Why do they always ask if they look fat?
Most women feel insecure. We are bombarded day after day with images of women who the media say are beautiful, and they look nothing like us . So we seek reassurance, and who better to give it to us than the people who love us?
Yes, we want to be told we are gorgeous, we want to be told we are beautiful and wonderful and completely perfect in each and every way.
But the question most of us are really asking is "Do you love me?". And when you say, "You look gorgeous", we hear "Yes, very much".
Oh, by the way, it is perfectly okay for you to say than another woman looks pretty -- as long as there is a follow-up that gives your lady the impression that the pretty girl is: "nothing like as pretty as you, of course"