Those browser vendors are also members of W3C. That's not why W3C HTML5 is irrelevant.
WHATWG HTML (formerly HTML5) is "rolling release"; the only version numbers are the "Last Modified" date at the top of the document. Meanwhile, W3C HTML5 has defined releases that are thoroughly scrutinized, reviewed, and debated in endless committee meetings.
One of these models is good for rapid-release and fast iteration. The other isn't.
Finally, W3C members are large companies, not individuals (with a few notable exceptions, like Aaron Swartz). WHATWG members are mostly individuals, many of whom are ordinary web developers who don't work on browser implementations. This difference is largely the raison d'être of WHATWG; it was the perception of many that W3C standards were diverging from what actual web developers wanted.
WHATWG HTML (formerly HTML5) is "rolling release"; the only version numbers are the "Last Modified" date at the top of the document. Meanwhile, W3C HTML5 has defined releases that are thoroughly scrutinized, reviewed, and debated in endless committee meetings.
One of these models is good for rapid-release and fast iteration. The other isn't.
Finally, W3C members are large companies, not individuals (with a few notable exceptions, like Aaron Swartz). WHATWG members are mostly individuals, many of whom are ordinary web developers who don't work on browser implementations. This difference is largely the raison d'être of WHATWG; it was the perception of many that W3C standards were diverging from what actual web developers wanted.