Activision Blizzard was also a founder and left the PCGA in 2009. The group's ultimate goal is simply to "ship better games" that are more fun and profitable.
Dell, Intel, Epic Games, Capcom, Razer and Sony DADC remain with the group as 'Promoters' while AMD has downgraded to 'Contributor'.
"A large majority of our members want to continue moving towards exploring ways to provide better leadership to the PC Gaming Ecosystem at large and use the data we've accumulated to make informed decisions to help ship better games," blogged PC Gaming Alliance boss Matt Ployhar recently.
He added that it was "premature to speculate" on the PCGA's next set of objectives but it would likely involve streamlining hardware requirements, tackling piracy and DRM.
"We simply want to ship better games, which are more fun, more profitable to the ISVs so they can hopefully keep feeding us more games, but also providing more value back to the consumers," added Ployhar.
Microsoft say they're recommitting to the PC gaming market and one of their first moves doing that is Lionhead Studios' Fable III for PC, which has no release date yet.