Nvidia seems to think that Quantic Dream's latest interactive storytelling adventure isn't a PS3 exclusive. They have the title listed as one of the games "current and upcoming" which can take advantage of their video cards' PhysX GPU-acceleration features.
Of course, we can't say with any certainty whether or not Heavy Rain is going to be available for PCs, but it makes perfect sense to me. Adventure games might not be the craze they were when I was a kid, but there's still a market for them and a game that is as ambitious as Heavy Rain could very well find success there.
PhysX Games List [Nvidia -- Thanks, Erik!]