My version of VLC is from before Apple opened up the new APIs, so is Movist. Playing the exact same HD h264 file in VLC, Movist and Quicktime X player results in the same CPU usage of 37% - 41% on my 3 year old, 2.8 GHz iMac which does not even have hardware acceleration for h264. Playing the same file through Flash maxes out one of the CPUs at 100% and the video stutters and drops frames.
Flash's problem is not about hardware acceleration. If VLC and Movist can achieve the same low CPU usage as Quicktime X player on the same hardware means it's not an API availability problem; it's simply crappy, crappy code used in Flash.
The version of Flash before 10.1 contained PowerPC code still for intel processors!