From this SOE forum post by Elidroth Renato (Doug Cronkhite), Asst. Lead Designer:
Pre-orders actually come from the days when we made a physical box that went on brick and mortar store shelves. We needed to get some idea of how many to manufacture so we didn't have thousands of customers without product, or have thousands of boxes sitting on shelves taking up space that places like Target, Gamestop, and Wal-Mart charge you money for.
Since we've moved to a completely digital product, there is no reason for pre-orders, AND it resolves the account issues that invariably happen every year of someone pre-ordering, our systems giving access to things, only to have their credit card fail processing for whatever reason (typos, denials, etc) and then losing ALL access to their account due to the system backing out the pre-order.
So this year, we've moved to a different system, with All Access members having the opportunity of getting in 2 weeks ahead of FTP players. Oct 28th, All Access players buy the expansion, and are in, immediately. FTP players can then buy the new expansion on Nov 11th. At least I think those are the dates.. I'll check again in the morning when I get to work. End result is a MUCH cleaner system and process with much less chance of problems.