I think they're just concentrating on producing enough iPads and not really focusing on cases, since the iPads is where they will profit the most. Look at it this way, would you rather have a case and no iPad or a iPad, but no case. There's substitutes for Apple's case right now and I say just buy one of those, or just wait a little longer and have the case shipped to your house in a week or so.
For Apple this may be true, but in "normal" retail the profit is in the accessories...
It is not like Foxcon is making the case however. And given the war chest of over $2B US Apple can crank up the production of the accessories. Though with the bad rep that the camera kit had on the iPod - Can understand Apple's reluctance to produce too many.
Add to that IMO is Apple building up supplies for the international launch in just 20 days. They are in a tough position I think. Supply the US market demand, or finally meet up pent up demand internationally for the iPad and accessories.
I think case studies down the road will show that Apple probably thought that the iPad was going to be just slightly a bigger success than the iPhone given the price points of the iPad. Surprise!
Again Apple came up with another product that we never knew we could live without.