Several people have told me they do the same. It might not be thousands, but there are programmers out there working like this.
It works for programmers because the iPad isn't your workstation, it's just your connection to a remote workstation. I'm not sure this is applicable to e.g. graphic design.
you know, working on a terminal (thin client) is nothing particularly new. and when you attach a keyboard and a mouse/touchpad to assemble a kind-of-laptop-but-not-laptop terminal it's by strict measures no longer 'working on a tablet', so what's the point of it exactly? carrying around a keyboard to say you don't use a netbook, it's a tablet? trying to prove something?
I hate to disagree with you because I abhor the idea of using a tablet for my work. However, it's still a machine that gets longer battery life than a laptop, is smaller (so theoretically more portable), lacks a lot of the power of a laptop, etc. It isn't the same as using a laptop. It's both more and less convenient.
It works for programmers because the iPad isn't your workstation, it's just your connection to a remote workstation. I'm not sure this is applicable to e.g. graphic design.