Gamesindustry.biz reports that Microsoft and NVIDIA have departed the PC Gaming Alliance, a movement the two organizations helped found. Neither firm offered a reason for departure. The PCGA was founded a couple years ago, if memory serves, to advance the PC as a viable platform for gaming. As consoles grow in market share, and development costs for PC (plus the ever-present threat of piracy) continue to spiral upward, the platform has long been losing its …