"The kindle can't check email (which is kind of bizarre for an EVDO device), can't browse the open web, cannot play music, and much much more."
Actually, the Kindle can do each of these things, although some of these features are neither elegant nor very quick. The subtext of your points are well taken: Amazon has soft-pedaled these features in its desire to brand the Kindle as a reader rather than a convergence device, much as it has always been important for Amazon to brand itself as a bookseller rather than a mega-mall despite its relentlessly expanding product mix. (I've sold 25,000 copies of a beta guide telling people how to use the Kindle's email feature, its web browser, etc. -- a niche created by the fact that Amazon plays the features so close to the vest! -- amazon.com/exec/obidos/ASIN/B0011XW1E8/EBEST)
More to your main point: yes, there are excellent openings for other devices to elbow the Kindle to the side, and Apple will surely take some of that space. It only makes sense that most of these devices, in time, will be able to purchase and download Kindle content from Amazon, which has and probably will keep a big lead in content selection. The Kindle has been a game changer because it has given traction to the e-reader concept after over a decade of others' false starts, but it is a bit of a Trojan horse: Amazon's longterm strategy is more about selling the digital content than about selling the device, and it won't be long before it opens the gates to a big tent approach wherein other manufacturer's devices are given the keys to enable them to sell Kindle content.
At that point, who wouldn't rather read on a i-tablet such as you describe? One important practical question will involve the cost of EV-DO service. With the Kindle, rather astonishingly, Amazon foots the entire bill. It's hard to imagine Apple doing that, but if it did....
Cheers,
Windwalker
What Apple Could Be Releasing, Part 1: Kindle Killer