One thing about the Apple tablet device(s) prediction I've already laid out doesn't ring true, that they (I'm predicting two) will run significantly different OSes, one a largely unmodified iPhone OS and the other a largely unmodified Mac OS X. If that turned out to be true, it would be a case of Apple missing an opportunity to do something unexpectedly better, which would be to incorporate everything that's unique about the iPhone OS into Snow Leopard, so devices running it were equally usable with a touch interface or with mouse and keyboard, and use that on the tablets capable of running apps written for either in a single OS environment.
One of the primary complications in doing this would be to make the responder chain not only pass both types of events, but work equally well with Mac OS X windows and iPhone OS windows, which are significantly different, with appropriate mapping of touch events to methods expecting key/mouse events and vice versa. (It occurs to me that the difference between Mac OS X windows and iPhone OS windows could be quite useful as if provides an easy way of checking whether interface translation is needed; simply test for the class of the window.)
This wouldn't mean the end of a distinct iPhone OS, since the resource limitations of smaller devices are still such that it makes sense to maintain a separate system for them, but it might mean that, even if it didn't come with the circuitry, you could connect a cellular radio dongle to your tablet (or MacBook) and use it as an iPhone.