IE9 lags way behind in HTML5 compatibility. IE10 will get over 300, but as you can see Firefox and Google are racing ahead.

http://html5test.com/results.html

Google Chrome 16.0 => 373

Mozilla Firefox 9.0 => 330

Opera 11.60 329 => 9

Apple Safari 5.1 => 302

Microsoft Internet Explorer 9 => 141