I think it's on purpose
I actually disagree with most of the people on this thread. I think Apple's shortages are perfectly on purpose. Here's my theory:
First and foremost, before anything else, Apple knows how to manage it's image. They've done a great job of making people want their products. They're not trying to simply sell iPads in the short term, their motivation here is more than that. They want the iPad to take over the market. They want iPad 3 to be even bigger than iPad 2. So why do they limit the market?
By limiting the market, you can do two things: First, you make the device more desirable to those who don't have it. People always want something they can't have. Even if they finally give up, and move on to another product, they're always going to wonder what they're missing with the iPad. If they wonder that, they'll eventually come back around and give it a shot.
Secondly, limiting the device somewhat will cause only those who _really, really_ want the device to actually go out and buy it. People who are only looking for a "tablet" device, and don't care whether or not it's the iPad, will ultimately buy the Xoom or something else. Sure, Apple loses their business, but guess what? Those people never cared anyways. What kind of P.R. could Apple possibly stand to gain from blasé users? Very little, indeed. They want their users to be enthusiastic about their device. Waiting for the device creates an attachment to the device before the device is even received. It builds a loyalty that's really hard to break in the long term. Hence the "Apple fan-boy". (How many Microsoft fan-boys do you know?)
Thirdly, limiting the device creates a community. Those who got the tablet are seen, in some sense, as outsiders, just like the kid who gets the Walgreen's version of the Wii instead of getting a _real_ one. Sorry, you're not in the club, because you don't have a _real_ iPad, you just have an "alternative". This desire to be in the club will ultimately drive the enthusiasm for the product higher and higher. Not only do you get to own something you don't have right now, but you also get to be in the club. Once you're in the club, you'll see the other members buying the upgrade, and so you'll want it as well.
Fourth, unsold iPads are liabilities. Apple has very little to lose by selling fewer, as long as all they produce are sold. Less revenue, sure, but less cost as well.
Lastly, scarcity drives price. The more scarce an item is, the more people are willing to pay for it. Plain and simple supply and demand.
It's genius if you ask me. Limit the stock severely, and then slowly, ever so slowly, increase production over a matter of years, not months. Apple has a long-term goal, not simply a short term one. Selling tons of devices right off the bat in the first few months is great and all, but they've done a good job so far of maximizing the mystery by not selling that many devices. Selling them heavily might work in the short-term, but Apple is interested in building interest over years, not just months. So, the device slowly becomes mainstream, but not before it becomes the stuff of legend. (Remember, a legend is easily broken by exposure.) And everybody wants to own a legend (I've seen people describing the iPad on this site as "amazing", "magical", "fabled", "legendary", etc. How many Dell computers bear that mark?)
And in the end, it wouldn't be that hard for Apple to spin up more factories, and for their suppliers to do the same. They just choose not to, in order to maximize the intrigue.
There are tons of reasons to limit supply, and I really, honestly, think that's what Apple is doing here.
I can't really blame them. They've got a great product to begin with. And I haven't even gotten my iPad yet. I'm still building allegiance before I've even received the thing.
