The audio capabilities of HTML5 suck. They're not going to get better for a while, and in the time it takes them to catch up, Flash will have continued to build on their well established foundations.

Okay, looking at HTML5 drum machines via Google. Here. Here's an one, http://www.randomthink.net/labs/html5drums/ - it's got all the basic trimmings, but the playback has tempo fluctuations, and the whole thing is slow. And this is a drum machine running all by itself. Compare that to audiotool.com, and tell me that HTML5 can do what AudioTool does.

Here's another one - http://pattern86.com/sequencer-in-html5/ - also laggy, and it only consists of four channels.

Keep in mind, I'm not trashing the efforts of the folks who made these, kudos to them! But compare that to something like this http://audiotool.com/app/dubtexno/1 -- HTML5 cannot do that. Sure, it will be able to in a few years. And surely, Flash will be able to do new things in a few years, too.

This doesn't even address the lack of a (for want of a better term) unified developing environment for HTML/JS/Canvas/Audio a la Flash CSwhatever.