The part of the post about the font rendering is BS anyway. The picture is supposed to show "sub-pixel positioning" and it only shows antialiasing (not even sub-pixel antialiasing) which as you've pointed out isn't handled by a browser anyway.
"Sub-pixel positioning" on the other hand would indeed need to be handled inside of the browser, so that the engine knows how much space something takes up so it can position the next item- But the picture accompanying the post is wrong/irrelevant.
Not sure I agree - most fonts are cached (as pixels) at a few offsets, so the ability to place a character is constrained by 1-pixel increments (or 1/3-pixel increments in the case of ClearType).
A true vector placement of each character gives you the ability to show type at any subpixel offset and then anti-alias, and I think there's a good chance they're doing this.
"Sub-pixel positioning" on the other hand would indeed need to be handled inside of the browser, so that the engine knows how much space something takes up so it can position the next item- But the picture accompanying the post is wrong/irrelevant.