Who cares about the decoder? 2.0 GHz Core 2 Duo can handle the decoding without breaking a sweat. Encoding 20 minutes of 1080p H.264 video, however, takes a fair chunk of time. Encoding is where we want to see some action. OK, nice _extra_ to free some CPU time when watching a video.. but typical use case is such that when you watching the video you don't have much else with HIGH realtime priority going on.
So.. encoding.. make it faster, make it smooth, make me cum!