Something else I thought of this evening (incidentally it was a Mercedes that cut me off on the freeway that jogged this).
This predates the separation, but it's telling. Gloria Trillo gave Carmela a ride home from the dealer (never mind that special snowflake couldn't stand to wait another 20 minutes). In that ride home, Carmela put on airs -- rich housewife, daughter at Columbia, huge ring, etc.
http://www.youtube.com/watch?v=cAdv8ipu4VgBeing a Mercedes saleswoman, Gloria had seen hundreds of nouveau riche New Jersey suburbanites, and really Carmela wasn't much different. She poked at Carmela's brags -- like purposely referring to Columbia as the Columbia School of Broadcasting. Gloria drops Carmela off, and at the end of the scene, you can just see her seethe at the Soprano McMansion. Here, they're sleeping with the same man, yet Gloria is without the things she really wants -- love, family, nice things, etc.
In Gloria's final fight with Tony, she ripped him for things that Carmela should have ripped him for:
"I'll sit back like a mute while you screw every woman out there."
"What'd you think that you could treat me like some stupid fucking goombah housewife? You think i'm gonna let some fucker shit all over me just because he buys me some ridiculous gaudy fucking ring?"
Despite her emptiness, she saw Tony and Carmela's relationship for what it was worth -- one not based on love, but rather on possessions. Tony could screw half of North Jersey, and Carmela would be fine with it, so long as she got her danegeld.
Some people might call that being a whore.