I think it might generally be the reason they're relaunching ALL the books, or most of them, in a few months time.
X-Men and FF were both finished at issue 100, and they're most likely being relaunched in some fashion sooner rather than later, and while I doubt Bendis planned on having Spidey included in the culling of the titles, he's getting a relaunch, too.
But yeah, unless they stick to the idea that the Ultimate books are for top-tier talent, which is one of the things that made the books attractive in the first place - It was Millar and Bendis effectively defining the Marvel Universe, but they spoiled it by bringing in the likes of Robert Kirkman, who does great work elsewhere but really, really screwed up on Ultimate X-Men - Then I don't see the Ultimate books, except Ultimate Spidey, lasting very long.