I didn't say that Jeph has "sold out", I just think that he has been increasingly writing to his new audience instead of his old audience.
Old audience: Indie rockers in their early-mid 20s.
New audience: Teenagers who think the bands mentioned in the strip are made-up.
Ok, I don't agree with the description of the "new audience" but sure, the comic moved away from its original concept and humor style to a more soap opera model. This happened a while ago. But you know what? This ALWAYS happens.
In every webcomic I've ever read that had a vibrant cast and plot arcs of some sort that depended on character interaction/evolution and wasn't a gag-a-day format. The original type of humor gets replaced, initial cast members get dropped, and thing... oh no! change. This isn't awful, it's just how it is, because most first concepts aren't fertile enough to carry on through in their initial format for longer than a year or two. At that point either you continue reading because you enjoy the new format, or you go away. But it's useless to complain in this case, imo. And also imo, QC is one of the better types of comics because (at this point) the soap opera is engaging and enjoyable. I have much more issue with comics that
don't go the soap opera route and instead try vainly to keep on doing their original format after the writer already burned out on it, without any of the charm or wit. Ie: most print comics in newspapers that started off cute and fresh, and are head-thumping dull after a few years. Actually, you'll notice that even there, a lot of writers switch to soap-opera after the first two-year period--this is just how storytelling works.
So the way it goes is: first mostly humor, a little story-->characters develop, soap-opera-ish story takes over-->soap-opera becomes ridiculous, everyone gets sick of the thing.
The first step is fine, the second step is fine too, and the "good" authors in my mind are those that can stop before the third. And I don't think Jeph is anywhere near the 3rd step yet.
(As far as webcomics go, I think "Boy Meets Boy" worked pretty well with this pattern: it started off as a humor comic, as the humor fell off it moved towards drama (and the drama was specifically provided to replace the humor as the main interest/draw) , and then the author ended it just about the time the drama was getting so thick it was about to consume itself. If anyone remembers the children's book Dragons series by Patricia Wrede, it was even applicable there: first book, clever and funny. Second book--less funny, but the romance and drama made up for it. Third book... um, ugh.)