Anecdotally, I know several people who have replaced their computers completely with iPads. They won't be buying new laptops any time soon (and yes, they use their iPads for work).
Granted, I'm doing development, but most tasks involving a computer are positively impacted by increases in screen real estate. I've had the bookkeeping office say they won't work with less than two monitors, and one of them needs to be largish. Given the spreadsheets they work with, I see the need.
There are plenty of tasks where the lack of real estate might seem to be unimportant, but what it comes down to is that when you're trying to fit anything of nontrivial complexity on a screen the size of the iPad, you use more and more mental energy on context-switching as the complexity increases.
If there are work contexts where the iPad is sufficient, it's not a big leap to imagine that there are even more non-work contexts where that is also the case.