And I'll give you a little technical reason for this. With PayPal, you can only "Authorize and Capture" with an honor period of up to 29 days. That means 29 days between the initial transaction and actually taking the funds from a customer's account. Right there, that one basic limitation prevents companies that take pre-orders from using any type of automatic charging with PayPal. To make matters even worse, for those companies who might only need 29 days, PayPal only guarantees the funds for the first 3 days - that means when going to capture, the money may not be there from day 4 to 29.
Taking a credit card (instead of using PayPal at all) can solve this limitation, but opens up all manner of other issues, especially when taking credit cards from other countries.
I've used the PayPal "Authorize and Capture" system a number of times in the past when I knew I'd be running out of stock and there would be some weeks before it was replenished. It's much better to put through this kind of transaction with the item listed as "back-ordered" than simply telling people to come back later, as many simply won't.