It looks like they are cherry-picking HTML5 features that IE supports, but Mozilla/WebKit don't. But I don't see much of the important stuff like tag support, web workers, geo-location, databases... MS is pretty much full of shit.
Note that they never say that they are most standard compliant browser. They specify the tests they are running and the % of them being passed.
Disclaimer: I know I might get down-voted for this but I work at MS(not in the IE team though :) ). Of course, my opinions are my own and not my employer's.