@mb: I wouldn't call title exclusivity a defining factor of a platform, as most games these days have multi-platform releases. I guess I'd also argue that PlayStation Now and OnLive are actually getting their own independent release of multiplatform titles. I think of it like a port, in that it's identical in almost every way but the mechanism by which you receive it is different. The original release of Killzone 3, for example didn't have the input latency of the PlayStation Now version.
@corruptedevil: Haha, true enough!
@jeff Wanna weigh in on this? How come Steam, PlayStation Now etc. are not considered platforms on the site? It seems like a pretty arbitrary definition, when PlayStation Network and Xbox Live are considered platforms, and aside from their integration into a console, they are identical to things like Steam, OnLive, and other similar services.
In fact, OnLive was integrated into an exclusive console at some point (maybe it still is), so that seems like a prime candidate for Platform-ization.
@ll_exile_ll Perhaps there should be a "Service" category for these various online distribution services. When this site refers to platforms, it seems like it is really referring to a physical hardware+software bundle (with the curious inclusions of XBL and PSN).