This only means they haven't shipped it yet.
It seems to me that (since your delivery estimate is 20th), you're in for release day delivery. In US, how this happens is that usually the order would leave Amazon warehouse on 18th or 19th with FedEx/UPS next day delivery and you'll get it on 20th.
On another note, Gamestop.co.uk ships the 15th also. Not sure how reliable they are, but there you go.
I just find it a little odd that every European Amazon is dispatching the game on the 15th and yet Amazon.co.uk dispatches them around the 20th. (Says 19th for me)
Oh well, I'll live.
O_o I preordered through amazon.de and after the order was received and handled I instantly received a email with preorder-access-codes and a download-link to the client. and the full-version-key will be shipped with the box on early-release, arriving on december 15th, for all german customers.
so germany won't have any fear of a downtime