They are the epitome of the camera-hungry, smug American host; they are the Alex McLeod/Paige Davis to Susannah and Trinny's Carol Smillie. They seem to think that they, not the woman being made over, are the stars, and they can't stop preening and performing for the camera. I don't think I'm being naive--I know that Susannah and Trinny are probably just as self-promotional as Clinton and Stacy--they have a book, after all--but the fact is, they know how to present themselves on the show so that they don't look like self-obsessed primadonnas. Whereas Susannah and Trinny actually look like they make an effort to make the woman feel attractive, Clinton and Stacy would probably drop their tiaras and run if the cameras weren't there.
And what's worse, they're really not very funny or bitchy--they're just fussy, and that's fucking boring. I know that people often complain about the Queer Eye Fab 5 being nothing but gay stereotypes, but really Queer Eye shows much more respect for the Fab 5 than WNTW has for its "fashion experts," Clinton in particular. It feels like Clinton's every move has been scripted to portray the fussy-but-sterile gay male without any of the individuality or personality that the Fab 5 bring to Queer Eye.
Postscript: I know What Not to Wear has been out for a while on TLC, and even been through several incarnations of hosts, but we just got TLC, so we're catching up.