Plain and simple. Publicity. If Bungie fixes the game before D2 everyone will think a little higher of Bungie. Which gives a long term benefit of guaranteed customers. As well as a bigger player base from good rep.
English
-
The thing is they won't. The amount of people that will "actually" leave to the amount of money the save is a drop in the bucket. This isn't monthly subs and it's not gonna hurt them in the slightest. If anything D2 will bring more people back because its aimed at starting from fresh, which caters to new players or players that missed dlc's. They won't do shit ... just watch.