Google+ finally rolled its online social games addition as an added feature earlier this week.  Google owns a stake in Zynga games as one of its biggest investors, and Google+ adding Zynga (and Angry Birds) to it’s online offerings is a natural extension of that relationship.  It’s also a move that could pose an impressive threat to Facebook and its social gaming. That’s because Facebook earns a 30% transaction fee from third party game developers — but Google collects only a 5% fee.   Some analysts speculate this is due to the fact that Google+ simply doesn’t have the user base bargaining power that Facebook has — but it’s obvious that the Google/Zynga relationship will play a deciding role as well.

At least a few start-up games developers are not convinced to start writing for Google+ just yet.

“Developing for multiple platforms and using multiple APIs is harder than people think,” Derek Irvine said.  ”Just because you have one killer game that’s working really well on Facebook doesn’t mean there’s not anything challenging involved in porting it to Google.  A lot of times, it’s like writing the code all over again. If Google were paying developers to come up with games for their platform, that might be different.  As it stands, G+ is a real possibility but not a big priority.  We don’t yet know if the users are numerous enough to support the games.”