Many in the HTML community have worked hard to make the vision of the XML community a reality. We did XHTML way back in 2003: The X-Philes. We filed bugs related to XML on browsers. We made sure that the DOM environment for XHTML shared the functionality of HTML so transitioning would be easier. We changed HTML so that in the DOM it appears as XHTML (i.e. namespaced). We changed CSS so that transitioning away from HTML would be easy. Ian Hickson wrote test cases for incremental rendering of XML. Henri Sivonen then fixed Gecko to render XML incrementally, making it more competitive with HTML. I wrote a proposal for XML that I think will give XML more traction on the web if adopted.
And yet all we get for working on their vision is shit. While our own vision is held up by a continuous series of roadblocks.