Tablets work fine for that though. (I have an Archos 5 I do exactly that with.)
Tablets that aren't pocket-sized have failed over and over again for very good reasons, gorilla-arm chief among them.
Why haven't they been successful?
For example: http://www.amazon.com/Nokia-N800-Portable-Internet-Tablet/si...
Things like the Archos tablets are much more realistic. My Archos 5 is great for web browsing, and I am sure the Archos 9 is a fine computer replacement. It hasn't caught on yet because it's not for sale yet.
I'm a little perplexed at how this device seems to generate such strong opinions and armchair quarterbacking. It seems to me that there is a lot of pent-up demand for a decent-sized tablet but people have been disappointed so many times they're a bit paranoid about it.
Even when the X10 comes out, depending on the screen, I may keep using the Archos anyway. The screen size is nice enough to watch a tv show and the resolution is great. The cell phone screen may be too small.
Yes. Especially when the more powerful, cheaper device is really bad at whatever this single convenience is, whereas the new product is very good at it, and the single convenience is important to the user.
See: Kindle vs. iPhone e-book reading.