No browser supports HTML5 completely correctly. Granted there are ones that do it better than others.
Partially because the final spec is just one day old. But in general, all HTML support is always just "really close." The closer the better, and that is what they generally compete over.
Agreed - and as we all know, until recently MS/IE just used to do their own thing, but now they seem to be at least trying to play better.
As far back as IE7 there has always been extra code snippets that will have to be added to deal with browser inconsistencies with HTML, XHTML and CSS. Most often MS was last to the party and only if you add proprietary coding.