Specifying codecs for the web

But none of the major vendors are likely to obtain HTML5 compliance, unless its by watering
down the standard to contain mostly SHOULDs that they can decide not to implement.

HTML is a very qualified success. Tag soup has won out for the most part. Things have improved
in the last ten years, but not very quickly. Can you think of a web browser people use that's
HTML 4 compliant? Not "nearly" or "sort-of" or "the important bits" but the HTML 4 standard as
published ?

Last time I looked Mozilla.org still had bugs open against rarely used HTML features dating
back to the start of the project in the 1990s.

I'm not completely sure I understand how this happened, but one thing that definitely had an
effect was the encouragement to "edit in Notepad" without tools that could verify the
resulting document meant anything, let alone what was intended by the author. Modern tools
have much reduced this tendency (most people now create content in Wikis or blogs where they
can type an ampersand without making the site fail validation).