It could be pretty easily argued that Blizzard is one of the biggest PC gaming development houses in the business today -- they consistently own both the sales charts and the playtime stats in terms of PC gaming. But Activision-Blizzard has quietly confirmed that they've passed on a membership to the PC Gaming Alliance, a group that claims to be "the authoritative voice on PC gaming worldwide." Activision, for their part, says that they just couldn't justify the membership fee, and this isn't the first industry group that they've snubbed: they famously left the ESA and their big yearly conference at E3 last year.
The PCGA claims that this isn't a big setback -- despite this and a few other losses, they say their numbers have grown, and they cite a few other big still-members, including Microsoft, Nvidia, and Intel. But given how much of an influence Activsion-Blizzard is in PC gaming, it's hard to say you're the "authoritative voice" of the platform when you don't have any formal connection to the biggest developer/publisher in the industry.
What does this mean to us players? Probably nothing right now -- the PCGA is right: the loss of Activision probably won't affect their work at all. But Blizzard, for better or worse, is being steered by Activision away from the industry at large. Right now, with events like BlizzCon and a huge reputation of their own, they don't need to be tied into these industry groups. But that may not always be the case.