Rumors of social gaming’s death may not be exaggerated.

There’s been increasing discussion about the possibility social gaming has finally jumped the shark this year, and Zynga’s big drop in daily active users sent investors in the social gaming giant rushing for the exits earlier this week.

And now comes news two of the game developers building games for Google+ are calling it quits. According to Gamasutra, PopCap and Wooga, whose games combined count more than 50m monthly active users on Google’s social network, have decided to remove their titles from Google+.

“We’re not really up for a conversation on that topic” a PopCap representative told Gamasutra’s Eric Caoili. “Certainly, Google is a valuable gaming partner for PopCap and EA, and we’ll continue to develop for Google platforms,” he added.

As Caoili notes, one of those other platforms is likely Android, Google’s mobile operating system. Which provides more evidence that gaming companies are rethinking their social gaming investments and instead starting to focus more on mobile opportunities. And perhaps for good reason: research firm ABI Research predicts in-app purchases will turn mobile gaming into a $16bn per year market by 2016.

Obviously, social gaming is a multi-billion dollar industry in its own right, but there are significant questions about its future. The biggest social gaming platform, Facebook, hasn’t yet figured out its mobile platform strategy, leaving game developers unable to tap into its rapidly growing mobile audience. And there are concerns that users are tiring of the world’s largest social network, which would obviously be bad news for those operating social games on Facebook’s platform.

With this in mind, it’s not entirely surprising that some of the developers which jumped on the Google+ bandwagon are reconsidering whether a Google+ investment is really worthwhile.