I think it has more to do with how society treats us as wives or mothers than our desire to define ourselves that way. If you have a child, with or without a spouse, every treacher calls you "Mrs". Or introduces you to the class, "And this is Jessie's Mommy..." (Kindergarten, preschool). And really, being called "Mommy" all day does have a certain psychological effect on you.
As for screen names, yes I've noticed that pattern too. I am not one of them. I've been "dezcordero" online since I was 16, and is the pen name I will use if I ever write my novel

I refuse to lose who I am to my kids, I think they will respect me more when they understand I am a person besides just "mommy".
Dez