A second-system replacement for the <audio> tag is more important than being able to render graphics or store data locally? Questionable ranking.

Decent summary of important stuff in/related to HTML5, though.

> A second-system replacement for the <audio> tag

I don't believe it's intended as a replacement for the <audio> tag. The audio tag exists to embed (pre-existing) recordings and their metadata (e.g. transcripts). The purpose of the audio API is generated sounds (music sequencer & the like) and low-latency sounds (for video games).

While you could probably re-implement <audio> on top of the web audio API, that's not very useful.