Well, since you get placed into a league by playing only 5 placement matches, there are bound to be some misplaced players.
Just think, what if all 5 of your opponents in the placement matches dropped out of the game? You'd probably be at least Gold.
BTW, I changed my avatar. Since I can't go for gold in the challenges right now, I'm getting my Spectre fix here
Edit:
Found something nice. It's a pretty in-depth FAQ about ladders and rankings and promotions. And it seems that promotions are allowed..