For all those suggesting a convergence between a tablet computer and a Kindle/e-reader device, have you ever seen an e-reader? Probably the most defining technology of these is they use "electronic paper" rather than a traditional LCD or OLED screen, which because it isn't backlit is much easier on the eye for reading large amounts of black and white text as it's the closest thing to reading real printed text on paper. However, it's currently monochrome and suffers from such a low refresh rate that it's totally useless for just about any tablet application - it really would be like having an original Newton display on a iPhone.
Sure you can read e-books on an LCD display, you've been able to do so for years on a raft of PDAs, but backlit display technology just isn't a good technology for this, hence the popularity of Kindle and other true e-readers.