One contributing factor, I think, is artists beginning to push beyond the 'album' boundaries, such as the way Radiohead released some of their recent albums or subscription-based monthly song things I've seen here and there.
I like the idea of a cleaner, buttonless interface (a la The Onion Wheel, I admit it), but part of why I like the home button on my ipod is that I can double-tap it to bring up the music options while I'm taking off my gloves in the winter. Guess I'll need to finally play around with that...
I would expect Apple not to mess with average release dates for new models (macrumors's guides are a good place to start), but I'd also expect a change in design by the time the Nehalem processors appear. The design is fine I suppose, but still identical to the old aluminum powerbooks.
I think that if you are planning to use it in the time between now and July 11, just fork over the extra $10 and laugh at the people who would be stuck waiting