This same listing mentions that Microsoft is "connecting players via the LIVE services on new devices beyond the console" and, more explicitly, asks for someone to "drive the platform and bring Xbox LIVE enabled games to Windows Mobile." The Principal Program Manager is expected to focus on "what makes gaming experiences 'LIVE Enabled' through aspects such as avatar integration, social interactions, and multi-screen experiences."
Granted, there's no way to tell how soon it will arrive, but it looks like Xbox Live and WinMo devices are destined to be together, eventually.
Microsoft Xbox 360
Microsoft Xbox One