Windows Mobile 6 still is powered by Windows CE 5.2 because at that time when it was developed the Windows CE 6.0 was not ready yet... but Microsoft is going ahead and continues to develop the Windows CE platform (cornerstone of each Windows Mobile phone):
Join us at the Windows Embedded CE 6.0 R2 Launch Event and get ready to build the next generation of smart, connected devices.
Windows Embedded CE 6.0 R2 adds even more exciting technologies to the CE 6.0 operating system - technologies that embedded developers can use to boost their creative capabilities and easily establish connections to Windows Vista, Windows Server 2008 and other devices.
This is a virtual event, so you'll be among the first to get up to speed on the latest features in CE 6.0 R2, right from your PC. There's no travel, no registration fees, and no downtime required - just sign up and attend from your office, living room, or any remote location.