I just watched this presentation on The Real Benefits of HTML5 For Games (http://vimeo.com/41825829) and there was a slide that said good javascript programmers do not necessarily translate to good HTML5 programmers.
Now, what exactly is a HTML5 programmer?
It's someone that knows a lot about the HTML5 spec. Where as someone writing a game in HTML5 will most probably be using only a handful of the features in the HTML5 spec, and it would most likely be the <canvas> element, some <audio> maybe localstorage, and that's it.
Where as, HTML5 programmers will know almost everything there is, and they are most likely subscribed to all the top blogs that talk about HTML5.