It's simple: Native HTML5 is powered by the cloud.

It means IE is not cross-platform. Seriously.

Taking a random stab: the fact that native apps—i.e. non-webapps—that embed the MSHTML web view control to render some of themselves, will now be capable of using HTML5 features in the pages they display within those controls, might get called "native support": as in "installing IE10 provides native HTML5 support to Windows."

They are trying to say it's more fit for HTML5 than Chrome. PR 2.0

It makes as much sense as the 'Post-PC world', just marketing fluff.