From people I've talked to in my family and others (non-technical folks) the idea of purchasing an iPad when it first launched wasn't incredibly alluring for anyone who's not an early adopter. Regular buyers like to wait until 1) reviews are available, 2) updates are out to fix bugs, and 3) the vague "quirks" are worked out in a device before pulling the trigger. $500-800 is a big investment for people buying a device to use on their couch, casually.

But now that the third generation is out, and it has an amazing new screen, great battery and extremely fast wireless (and, presumably, no "quirks" that people might think had been present in the earlier models) it's thought to be a safer buy. It's not the first model, it's been out a few years, Apple knows what they're doing by now, they've seen commercials and know people that have one, etc. So what were they waiting for? The new one to come out. And it has.

I think the buyers this weekend weren't merely Apple fans with iPad 1s and 2s who wanted to upgrade, but lots and lots of new owners who have been waiting patiently for a good reason to whip out their credit cards. For this reason I think overall sales of the new iPad are going to be totally insane.