Bungie explains why there's still no PC version of Destiny Eurogamer.net
Parsons also said creating and releasing a PC version of Bungie's shared world shooter would not be as easy as many believe, because all versions of the game connect to the same persistent video game world, which itself extends to multiple platforms.
"It is not nearly as simple as you think," he said. "It is one central world no matter what the platform, and so that
requires lots of intensive thought.
Seems the reason this is not on PC, is because its cross platform on consoles. And PC players would have an unfair advantage with cross platform. and they don't want to have separate servers for them or something.