I don't know. I may be suffering from sample bias, but around me, everyone who have iPads and iPhone change models as soon as one comes out. And they feel an URGE to do it. For reasons I cannot understand.

I've also heard the same story from other friends in different places, so I can only assume that a large amount of pre-iPad owners seem to buy a new one systematically. I don't have market research data to prove anything, however.