It's almost like they plan on this issue...
Apple marketing is very predictable these days.
1) Create a new product.
2) Release controlled leaks and rumors.
3) Make a well orchestrated, public release in front of media.
4) Announce a release date and allow pre-order.
5) Announce inventory ran out, regardless of the volume of sales, before the official release date.
There's no reason for Apple or anyone to oversupply on opening day. In Apple's case, by shutting down preorders they generate press just because they're declaring it full. If you open a site to beta traffic with signup, then get coverage at a place like Techcruch, and shut down signups with only 10 users but don't delcare it, the press will think you're a hot item if you don't provide numbers.
That isn't exactly the case with Apple, of course -- they are a hot item. Without numbers, though... they could have sold 10 or 10 million. I'm sure the other estimates made in the thread circling 250,000 are close though.
I'm pretty sure there is value in creating the _perception_ of scarcity (nee exclusivity) for one's product... but that should also be conveyed in the price.