I could argue that W3C didn’t follow that policy when they attempted to push xhtml, which completely inverts that priority order, as xhtml is bad for users and great for purity.

But instead I’ll point out that W3C no longer maintains the html spec. They ceded that to the WHATWG which was spun by the major browser developers in response to the stagnation and what amounted to abandonment of html by the W3C.