They are only running out of the 3G models, NOT the WiFi models. They didn't sell a million 3G models. They just didn't make enought 3G models.
Remember that Tickle Me Elmo also sold millions and people went crazy for it in it's day for a SHORT period, but then fizzled like a lot of overhyped product.
BTW - I actually HAVE an iPad. I do like it, but it's just a big iPod Touch really. It's fine certainly and there's nothing wrong with it being just a big Touch, but not worthy the frenzy that's is perceived currently. The size is really the ONLY innovation here that didn't exist before in the Touch. Obviously, size seems to be important to people, but I think after some time after the initial frenzy of having a new toy, people will figure out that this is an expensive and too heavy book reader, not as good a game machine as the PSP, and not have the convenience of always having it with you like the iPhone. It'll fizzle out in a couple on months - not completely, but to normal netbook-ish sales levels.
Tony