The "disappointment" of a few people about the Wii U visuals we saw at E3 isn't originating from a hypothetic lack of power of the system. It's for the most part, from the projects showed, as a large bunch of them started their development on previous platforms, sometimes on Wii. Games tailored from A to Z for the Wii U will take advantage of its noticeable leap in capabilities compare to the current gen HD. For another part, it comes from the dev kits themselves, the hardware inside, their freshness as the newest were supplied just a few weeks before E3, even days for the special drivers, Wii U discs, and the final form Wii U dev kits with a built-in drive. There will be AA in launch titles. There's no doubt about it, can't be more specific than that sorry.
But i must admit that they could have been more proactive in their communication during the show, explaining how it's work-in-progress titles, how some parts are still in flux, in completion, how it will be more impressive at release, etc.