It's currently easier to get a HTML5 game working in IE10 than it is in Windows Safari, for what it's worth. But I think I agree with your premise that HTML5 game developers aren't really targeting Internet Explorer in general. People who care about users on IE seem to be sticking with Flash.
I don't really see the point of comparing IE10 (just released) to a browser that has a minuscule browser share and hasn't been actively developed or updated in something like 6 months.