It sounds like there's third-party, closed-source stuff in there...

"Gmail voice and video chat incorporates Vidyo technology which is covered under pending U.S. and foreign patent applications."

EDIT: Wow, that's frustrating. The PC client says that the tablet is calling, and lets you answer the call, but then the tablet keeps ringing, as if the PC didn't answer. The PC also says that "video is not available" for the caller's client.