Google Sync was designed to allow access to Google Mail, Calendar and Contacts via the Microsoft Exchange ActiveSync protocol. With the recent launch of CardDAV, Google now offers similar access via IMAP, CalDAV and CardDAV, making it possible to build a seamless sync experience using open protocols. Starting January 30, 2013, consumers won't be able to set up new devices using Google Sync; however, existing Google Sync connections will continue to function. Google Sync will continue to be fully supported for Google Apps for Business, Government and Education. Users of those products are unaffected by this announcement.
While iOS users will still be able to use IMAP, CalDAV and CardDAV to access their information on Google, Windows Phone users aren't so lucky. Microsoft does not yet support CalDAV or CardDAV on Windows Phone 8. In addition, IMAP access to email does will not support push; although, that is a lessor inconvenience.
It's unclear why Google is dropping support for the protocol but the decision is speculated to be part of a feud between the companies.