I've ordered a Nook Touch for rooting and development work, and to find out how well this theory works in practice. Maybe in a couple of weeks I will eat my words ;)
However, for the sake of argument, let's assume that people do mostly read on their tablets. Unless B&N did something to the N2E that I'm unaware of, Android doesn't really do page-based scrolling. That's kind of what I was trying to get at with the horrible refresh rate comment- even if it can technically do email and social networks, it's not going to be a great experience (kind of like the Web on the Kindle). Here's a video of Angry Birds on the N2E, as an example: http://www.youtube.com/watch?v=k22BB8VPI5o
(Edit: I do seem to remember that the N2E has a web browser built-in, so, assuming that it has pagination, that would work alright for email/social networks/HN. Though, IIRC, it's a slightly hidden feature- even B&N doesn't want to admit it's in there: http://www.barnesandnoble.com/nook/container/standard_bothna... (#10) )
I didn't mean to make that comparison, I guess. I specifically don't own a tablet because it doesn't offer any really appealing use cases to me. I can't speak for the market in general, the iPad is a big-selling device, but e-readers are quite popular too[1].
I guess I want to wind this up; I never intended to lay in to your criticism of the eInk screen, simply to offer that my experience of people's use cases differs to yours. It's kind of redundant right now anyway, the number of hoops you have to jump through to turn a nook touch into a general-purpose Android box means that it's still not a consideration for most users.
[1] a quick google for "more tablets than ereaders" yields the converse http://www.google.com/search?q=more+tablets+than+ereaders