I find that in shows like Friends, Will and Grace, HIMYM, Sabrina etc etc, or most sitcoms I guess; the characters seem to go through a couple seasons of human-like development, they're not always "on". Then, later on, they become a complete stereotype of themselves, just solely acting out the characteristics that the public have responded to positively.
I think the issue with this show is that the characters were already at this slight stereotypical stage when it started, leaving little room for much movement in the storyline/character development.