For most of its existence, Facebook has had a stranglehold on social gaming. Google (Nasdaq: GOOG) and Zynga are slowly changing that. Earlier this week, the companies announced that Zynga's most popular game -- the metropolitan simulation called CityVille -- is now available on Google+.

CityVille joins Zynga Poker, which debuted last month at the unveiling of Google+ Games.

The search king hosts only 18 games so far, but the wins are notable. Rovio's Angry Birds joins CityVille and Zynga Poker. The only hitch? You can't take progress earned on Facebook over to Google+, even if you play CityVille on both platforms.

Even so, moving CityVille to G+ is notable for two reasons. First, it shows Zynga won't confine its most valuable properties to Facebook. Second, it shows that Google is serious about building up G+ as a gaming platform. Next step? Get Electronic Arts (Nasdaq: ERTS), Take-Two Interactive (Nasdaq: TTWO), and other social-game developers to commit to G+.

No one should be surprised by any of this. Zynga needs a diversity of players to increase the value of its platform. Google needs to convince EA and others that G+ is a viable Facebook alternative, which is why we're now hearing that G+ will soon support brand-specific pages. Expect Google to push EA, Take-Two, Zynga, and others to build G+ pages and embed direct links to their G+ games.

But in the end, this is a bigger deal for Zynga than for Google. Anything that allows the soon-to-be-public social gamer to grow independently of Facebook is a win. Do you agree? Disagree? Please vote in the poll below and then leave a comment to explain your thinking.