Carrying around both the tablet and a separate keyboard would be such a drag, though. I think people misunderstand how people use their netbooks. I have no official stats, but I suspect many of those who also own the "main" computer, be it a full laptop or a desktop, spend even more time with their netbook than with the "main" one. They might not admit it, because that sounds cheap. But when your netbook can do pretty much everything you ever do with a computer (including typing, a lot), and when you have all the motives in the world to carry around your netbook instead of your "main" laptop (much more portable, so cheap that you wouldn't mind it that much if it's damaged, etc.), that's just a natural consequence.
I think people type on their netbook a LOT more frequently than you think. The netbook is effectively their main computer in so many cases.