Even the W3C is not pedantic about "HTML5". A lot of what is advertised on their logo page at
http://www.w3.org/html/logo/ (File APIs, IndexedDB, WebSockets, SVG, WebGL, CSS 3D, etc, etc) are not technically part of the HTML5 standard specification (
http://www.w3.org/TR/html5/).
As another example, look through the presentations on "HTML5" given at Google I/O. All the interesting stuff is not in the W3C HTML5 specification.
There are numerous other examples.
Try reading through the whole W3C HTML5 specification (http://www.w3.org/TR/html5/) and you'll realize how little of what people refer to as HTML5 is actually contained in that document.