Why is there a limit?
Does Apple plan to ration them?
Gray market. They're going for very high prices where they are unavailable.
Does Apple plan to ration them?
It's the same thing that they did with iPhones. It's to prevent them from going in mass quantities to other countries where they go for five times the cost of what they are here...
When Apple's supplies catch up with the demand, and when they get them selling in the various countries, there won't be any permanent limits any more.