Seeing as the itunes app is wi fi only and apple want to push movies etc to as many people as possible isn't it feasible to imagine that video's will be next on apples wifi store.
Yeah, doubt that would happen anytime soon. Having the iPhone on for the entire download time for the video would drain the batter more than I think Apple wants. At some point when battery life is long, flash memory huge/cheap, and super fast wifi becomes the norm, it might happen.
I've found it no problem to stream a long video. I've streamed the whole March 6th Event from apple.com in it's entirety a few times, with not much fuss. Streaming is essentially downloading without saving to the device, right?