Those who don't "understand" tablets don't understand long car rides, having children, convenient internet browsing, watching videos on break at work, how-to's when working on a car, keeping entertained at a boring party your wife forced you to go to, and of course when you're on the porcelain throne.
Tablets are luxury items. It's for people who can afford to have one for convenience sake, and I have to say I find it very convenient in many cases that some of you people fail to see.
Does it replace actual computers? No, it never will. It will never replace my desktop or laptop. But for some of the reasons I mentioned above, it's actually useful if you find ways to use it. I don't know what I would do if I didn't have my iPad 2 to put on Sesame Street to keep my daughter occupied while I'm working on something.