It's unclear who led Girlfriends' formation, whether Kelsey Grammar rounded up a bunch of African-American heavyweights to build a show, or whether the heavyweights leveraged Grammar's success to get their show aired. Either way, Girlfriends operates at the peak of Hollywood production, with a VERY richly talented team of actors, writers, producers, etc.
The result seems much like Frasier, blending stereotype, caricature, and "comedy of manners" humor with delicately woven stories of challenges contemporary audiences will see as "real" and relevant. That's a tightrope walk. The humor is an established art, in accomplished hands; but the right compromise between humor and realism is far less certain, even for such a skilled group.
Though I might personally prefer to tweak the compromise a bit more toward realism, that would make it a different show. I really like Frasier -- familiar eccentricities/caricatures and all. But I find Martin Lawrence, Tyler Perry, and Eddie Murphy far too silly/campy/ghetto. I did, however, notice that they continue to make more money and garner more fame than certain others. The very-accomplished-but-not-as-famous crew behind Girlfriends surely notices that too.
Creators for HBO & Showtime craft shows to build on the networks' reputation for more weighty/intense/realistic programming. (e.g. Soul Food) Girlfriends' creators must likewise craft the show for the very different market positioning at UPN.
I expect the Girlfriends we see is a very deliberately crafted balance, adjusted to maximize ratings/earnings in a UPN context. The same could be said of Frasier; and I find both shows entertaining.
Male character construction in Girlfriends is an interesting side note. William is given more development & air time than any male on Sex & the City or L-Word, serving as a foil not just in interaction but in his parallel story lines. In making the story about the girlfriends, the writers have wonderfully shown no urge to regurgitate the standard set of negative black male stereotypes. Even more than with Sex & the City, Girlfriends mostly explores the leads' "issues" by contrasting with normality in its male actors.