It's not "free." You still have to buy cards and those that purchased the retail package got 4 starter decks (instead of 2) and 3000 "bf points" which are used to buy boosters. That many points is worth 30 dollars.
I really have no idea. It is just that there seems to be some confusion about this. http://forums.steampowered.com/forums/showthread.php?t=816710 and http://www.twcenter.net/forums/showthread.php?p=4606225#post4606225
Sometimes the cdkey can be linked to a specific region. For example Sacred 2...