First of all it would let women know that they are doing what makes their men happy, and second, believe it or not, many woman find it to be a big turn on. Well usually i do talk during sex, I tell my hoe that im about to bust a nut on her leg and stuff, and tell her if we're sucking not fucking take off the rubber. I believe the reason why more woman moan is they think it will boost the guys ego and that can help her sex life because he is more confidant in his abilities. Personally I don't really do a lot of moaning except when my girlfriend really hits something good. I had to wipe the jizz off my keyboard.
Some women barely make any noise during sex, and others scream their head off.
For example, I'm very quiet and my friends all say they scream. Its the same with guys. Some are real quiet and others are very vocal. Also, I think guys don't say what they like because sometimes they are afraid of upsetting or offending their woman. But it is nice to see a woman with such an open mind.