I'm surprised that they're going full HTML 5 as opposed to just HTML 5 for the control layer while having a Flash core to play the audio.
I don't listen to music using the flash interface anymore, the biggest problem is that after just an hour or two of listening the flash application is using a HUGE amount of memory and is hogging one of my cores at 90%. Flash on Mac OS X was never anything to write home about ...
Video is simpler: you normally play one video at a time, for long time periods. Audio tends to be used to play short clips simultaneously, and if the browser drops some or delays them, it ruins the effect.