After spending ten minutes with an iPhone 4 screen, then ten minutes with the iPad's blurry, low res screen, I can't imagine Apple will wait more than 24 months (summer 2012) to double the iPad's resolution.
I think that Apple knows that it is imperative to bring this resolution to the iPad, especially for the iPad's killer apps, web browsing and reading. The iPad screen is beautiful but the iPhone 4 makes it look really second rate, which is sort of a problem for would be buyers like me: now I can't buy an iPad until they up the resolution. In my defense I highly doubt the iPhone "5" (and hence "HD" iPad) will have a higher resolution screen in the next 5 years. So once I buy an "HD" iPad I can keep using it knowing that it is unlikely they will up the resolution again for quite some time, if at all.
Reasoning: I'm really really near sighted and holding the iPhone 4 inches from my face I could hardly see pixels -- I mean, they exist, they are just irrelevant, nearly arbitrarily small. Can you tell laser printer output (text, say) at 300 DPI from 1200 DPI? Doesn't the quality of the paper effect whether upping the resolution is even useful at that point? And lastly, the quality of the iPhone screen is even more amazing than good professional digital photo prints, which are significantly better than good color laser printer results or even good color photos reproduced in big hardcover coffee table books. I mean, if those photo prints (photochemical and laser offset printing) haven't improved significantly in terms of resolution in decades (because they are "good enough" and because it's sort of reached a plateau based on physics and psychophysics) then will manufacturers of LCD screens really need to go past that 300+ DPI point? (640 KB ought to be enough, right?) ↩︎