Could the launch of 'Old Republic' be what spurred this on?
It's been a long while since an MMO came along that even stood a chance at usurping 'World of Warcraft' but Bioware's 'Old Republic' is looking very dangerous for Blizzard. It's better than 'Star Wars Galaxies' - that's not saying much, is it? - and there is a crazy amount of attention being paid to it.
In a move that almost certainly stems from the upcoming 'Old Republic' launch, Blizzard is offering a free copy of 'Diablo III' to anyone who signs up for a year of 'World of Warcraft.' You don't have to pay all at once, but you do have to sign up for a full year.
In addition to 'Diablo III,' year subscriptions will net you a special mount and guaranteed access to the beta test for the upcoming expansion.