Well, to add a pair of guess, it makes everybody happy:
- SE side: preorder means getting money even before the game is on air. When we talk about a big company (and big money) a day or two can make a huge difference.
- Players side: the most of us loyal hype driven gamers are glad to have the possibility to access the game as soon as we can.
I think if they say something like "Give us 10€ now to start playing tomorrow" many people would do it right away! Nothing against it. Just felt like sharing my 2cents.