IIRC it's G72M, which is 7400Go, not 7300Go.
With a 1Ghz Dothan, they've either optimized the piss out of their H.264 code or they're using the GPU (which supports H.264 decoding acceleration). Given that the rumors say the delays were due to video drivers, I wouldn't be surprised if it's the latter. But if it is the latter it should be able to do more than 5Mbps/720p; again that may be a driver maturity issue.