During today’s WWDC keynote, Apple gave some demos of the sharing features in the next versions of their desktop and mobile operating systems, including deep Facebook integration in iOS 6. One thing they didn’t mention, however, was the same Facebook integration for the Mac. As it turns out, there’s a good reason for that. The version of 10.8 that launches next month will not support Facebook.

According to a tiny banner hidden on Apple’s OS X Mountain Lion website, Facebook integration won’t be available in OS X until this fall. Conveniently, that’s the same timeframe given for the iOS 6 release, and the presumed timeframe of the next iPhone launch.

Oddly, Mountain Lion Developer Preview 4, released earlier this evening, does contain full Facebook integration. Why Apple chose to omit this feature from the shipping version is a mystery, since it seems to be functioning well in its current form. Perhaps Apple’s agreement with Facebook is to launch all integration in fall. For example, iOS 6 launches in the fall.