The profit on the $499 iPad is probably no more than about $150 per unit. They may save some money since they are using their own processors. Which isn't too bad a deal for you, since Apple had to develop the thing and its software. I'm sure we'll see when the breakdowns inevitably come.
I'm wondering if the iPad could be close to a loss-leader (like the Sony PS3). Apple know they're going to make money back through the iTunes store.