It's worth mentioning that this is a biased site however. It gives Safari poor marks for not supporting Ogg Theora in video and audio, when in fact it's not required to support those to be 100% compliant with HTML5.
It's more of a handy HTML5 support checklist (because you need to support
some video and audio codecs even though they aren't in the spec), than it is a "test" of HTML5 compatibility.
Edit: it would also seem there are lots of HTML5 elements not listed.