I think we're experiencing an issue with the semantics of "niche". By niche, I don't necessary mean small. I mean specific. If you're rich (pretty much all of us here, I'd reckon), you get to have the iPad as a media consumption device, or as a stop-gap between your computer and e-reader (like me!). It's for people who already have 2 or 3 computing devices. That's pretty niche, even in North America.
As far as the success, I believe (my opinion, obviously) that many people bought iPads with the intention of replacing their laptops. These people have discovered (or will) that that isn't very practical. In my line of work, I sit in an inordinate amount of meetings. When the iPad came out there were so many people tap-tap-tapping away on their screens, taking notes. Today, there are far less; most of those people are back to their laptops. It's just an anecdote, but my personal experience is the same.
Who knows, maybe this is our aversion to change? I don't doubt that tablets are the future.
