There are three factors here: one, that eInk readers are cheaper; two, they are REALLY better; three, the battery lasts A MONTH... now, a tablet can't compete with that. I have two Kindles, an Android Tablet, and an iPad. And I am also weird, because it does not hurt me so much reading on the iPad (or even in the laptop). But I will buy one or two more kindle/nooks this year BECAUSE it is so awesome to read on them. And because they are really good to take on a long trip, even if I am going to the farm. And because they are no-distractions readers (when I am reading on the iPad, either I have to turn off wireless/3g beforehand or I get email/social notifications from time to time....)
So, no, $200 tablets will not take the place of $70 eInk readers so soon.