Microsoft has completed the update which Windows Phone users would need in order to continue using Google services, which has been slowly rolling out as GDR 2, but not all users have gotten the update yet. So, Google is granting another reprieve, and has decided to extend Gmail and Calendar syncing again, this time until December 31st. Microsoft believes that by then, the majority of the Windows Phone ecosystem will have been updated to support the DAV open standards.
This is just another in a long series of troubles between Google and Microsoft. Google has been refusing to build apps for the Windows Phone platform, citing the platform's low user base as reason that the development expense isn't worthwhile. Microsoft has tried to end-around Google and bring full YouTube to the platform, but Google shut that down for unauthorized use of the YouTube APIs. The two sides do seem to be working together on this syncing support issue, and have been said to be working together on a new YouTube app, but things are obviously not going smoothly.
source: The Verge