They have rankings by nation in addition to the overalls. Their base is far from a scientific sample, but I think they give better ballpark figures than some give them credit for.
Their "what's hot" section often has stuff about wordpress and the like, so there are obviously many webmasters. There is plenty of American Idol and all that, also. I have no idea, but I'd guess they advertise the toolbar in different places and maybe allow it to be bundled with screensavers or whatever.