Isn't contrast pretty much limited by the pearl screen? Somehow, I doubt if amazon is holding back the contrast on purpose. Like hey it goes to 11, but 10 will be good enough for our lusers.
Otoh, there are times when the book specifies grey text, in which cases it is useful to have a feature to force black text. I'm not aware of ebooks doing this, but PDFs definitely do.
I'm curious to see how the new Sony and kindle look side by side. Amazon has thus far avoided touch screen, but if Sony has managed to maintain the display quality with the new touch reader, then expect amazon to follow suit. I'm pretty sure the same folks who pooh pooh touchscreen Ui now will shiver to think how we put up with the DOS 3 interface all this time.