For example, even if you look at a show that many of the bashers seem to like -- Buffy the Vampire Slayer -- you'll notice that the speech of the characters is not entirely realistic. Xander is much more witty and Willow much more erudite than your average High School student. These characters also talk like people older than they are. And yet Buffy's dialogue is fun, amusing, where Dawson's Creek's dialogue is, at times, more annoying that the proverbial fin more annoying that the proverbial fingernails scratching on the more annoying that the proverbial finblackboard.

Well, it is exactly what the name implies. It is dialogue which is based, not on the way human beings actually talk to each other, but on the cliched expressions of self-help psychology books. The fact that Mr. Williamson et al use this type of language says a lot about their approach to character as well as language. Let me give you an example.
Perhaps you'll remember the episode where Jen tells Dawson that she is not a virgin but that she had already had sex at a very early age, an age when she was still really too young to have sex and that it was a bad experience for her. Now, a real human being might tell this to a friend/boyfriend in the following manner.
"The first time I had sex I was 13. The guy was a real jerk. I was drunk and we just sort of did it. He didn't even care if I enjoyed it or anything. I don't think he even cared if it hurt me."

Instead of herself, Jen is now merely "The Young Woman who Was Sexualized Too Early;" she becomes the title of a chapter about girls like herself in a self-help book. The moment the show's writer starts writing about her like that, he or she loses his or her connection to Jen's humanity; Jen is no longer a girl who endured something; she is just a piece on a psychological playing board, to be moved around as the plot demands.
Real people, especially sixteen year-olds, do not refer to themselves or even think of themselves as a self-help-book type. Yes, Jen is a girl who was sexualized too early. But if she is to have any resemblance to a real human being she must also be more than that, just as each of us is more than the problems you or I have that can be quantified in simple, self-help-book terms.
Other scenes pop to mind that suffer from this same problem, for example, Pacey's lambasting the teacher he had an affair with, accusing her of suffering from "aging issues," and Dawson's insults directed at his mother for having an affair. If you wrote down the words these two were spouting during those scenes, you could run over to your local bookstore and find them in any or a number of paperbacks in the self-help section. So why does the show suffer from this disease? Do the show's writers chose to write this way, or are they simply bad writers?

Well, I think both are true.
You see, it is easier to people one's fictional universe with psychological abstractions; when you eliminate ambiguity and complexity things go a lot faster, and TV writers face tough deadlines. It is much easier for a writer, instead of having to feel for Jen, to imagine what she went through and how it felt for her to go through it, to simply say, "this is the girl who was sexualized too early," just like the network exec says, "this is the commercial for Kellogg's which comes right after the commercial for Nike."
To be fair, clearly there are moments when the show doesn't do this, when it doesn't fall victim to psychobabble, when the writing is pretty good and the young actors do an admirable job with it. But overall, I think that if the show's writers got their hands on the theme song, you know, the Paula Cole song which goes:
They'd change those direct, simple and honest lyrics to:
Yeah. Sing it sister.
