Like the first Apple, the iPad is a miracle of tightly integrated design, giving maximum power from minimum hardware. (e.g. custom A4 processor for 10 hours of HD playback.)
Web apps will be too slow.
Eventually, hardware will catch up, and less efficient but more modular designs will be fast enough (as with the first Apple).
I don't think I'm making a big leap to speculate that this means the iPhone runs javascript comparably to the consumer-level (read: cheap Best Buy) desktop running some version of IE that most people have.
Considering the iPad's processor is significantly faster, I see no reason why web apps wouldn't run perfectly well on it.
Web apps will be too slow.
Eventually, hardware will catch up, and less efficient but more modular designs will be fast enough (as with the first Apple).