I understand Blizz may not want to dedicate resources to maintain an old OS, but why disallow the entire program to be run on the old OS. You can simply put a disclaimer that your OS version is out of date and known issues/bugs will not be looked at, use at your own discretion etc.
This mac is still a great little machine, but this planned obsolescence companies do is bull$$$$.
If all else fails, is there a date when battle net will completely stop working on OSX 10.6.8? (Hope it's much later than Soon®)