I don't think anyone is "above" co-writing. Johns and Bendis are Marvel and DC's current cash cows and they've both co-written books pretty recently.
DNA co-write the cosmic books and they are some of the best stuff Marvel's putting out.
Sadly, Abnett & Lanning are not real "cash cow" writers for Marvel right now. That said, I think WAR OF KINGS outsold expectations, which will help keep the space line safe. Joe Quesada personally stated 2010 having more focus on space stuff at the NYC screening of "PLANET HULK".
I was agreeing with the idea that Dan Slott deserves another title besides ASM, and if he is capable, should have one, whether an Avengers book or another volume of The Thing or whatnot (c'mon, it has been ages since I mentioned THE THING). That said, Slott and Gage work well together, and if "AVENGERS ACADEMY" is happening and the two of them were to work on that, it'd be cool.
Bendis even has co-written quite a few books in the last few years, such as THE ILLUMINATI with Brian Reed and SECRET WARRIORS with Johnathan Hickman; for the latter, Bendis has all but said that his name is mostly there to sell comics and Hickman runs most of that show.
I guess you gotta hand it to editor Steve Wacker for running a tight ship. You've got a 5 writer rotation that you have to match up with 5 different artists. The guy could easily be an MLB manager/pitching coach.
Yeah, I have heard that Wacker's feat of keeping ASM on schedule for so long and counting has been a "yeoman effort" thus far. Considering that work-load, though, it may be a while before another editor wants to make another weekly book.
Because, well, AVENGERS easily could be a weekly title. 2 weeks are Bendis, one is Brubaker, one is Gage and/or Slott. You can either buy them all, or only buy the issues of the creative team you want. It really wouldn't be a whole lot different than what is about to happen now, only with one title. Some have suggested the X-MEN books should have done that five years ago. But given that ASM's sales, while good, haven't been CIVIL WAR good and Steve Wacker almost has to clone himself to keep ASM going even at 3 issues a month, I don't think any other editorial teams are going to volunteer for another weekly title anytime soon.
(Although if the same editor is handling all of the Avengers books anyway, it really does seem silly to give them all separate titles, especially Bendis' books.)
Plus, DC running it into the ground with their last two weekly series doesn't help.