That is the most charitable reading, and how even that reading is supposed to be meaningful is beyond me. Basically, since MS can't demonstrate in any meaningful way that their not-cross-platform engine does anything better, they're offering up "it runs better because it's made for Windows" as a truism.
That's all the "native" label means, unless they can show that by making it "native," they get better performance than cross-platform browsers.
This is not the same thing as adding proprietary extensions to HTML5 that people seem to be inferring. Although IE9 doesn't support all of the HTML5 spec, so far as I've seen it hasn't added anything proprietary or invalid according to the spec, I don't see why they would change this for IE10
Then what they need to say, if they can prove it, is something more like "IE is faster than Chrome." If they're doing that at the expense of being single-platform, that's a tradeoff, not a feature to announce.
And if being single-platform doesn't make them faster than Chrome, what does this announcement mean? "Despite making this tradeoff, we are still bested."
My main point though was that all this talk has very nothing to MS introdcuing non-standard html5 in IE10, which loads of people seem to be implying.
I assume they also want to add "features" onto HTML5 too, in a similar fashion to ActiveX.
Its just the way Microsoft think, they have a very proprietary mindset, IMO.
One would expect "Microsoft adding features to HTML5" to involve something other than participating in the cooperative advancement of a nice universal standard.
[0] http://blogs.msdn.com/b/ie/archive/2011/04/12/native-html5-f...