The standards are a joke
You're not a web developer are you? Have you even read the standards?!?
No browser exists or has ever existed that supports the standards in their entirety. And it's a good job, considering that XHTML 1.0 - the W3C recommendation since 1999 - actually breaks the HTML standard! Any browser that bothered to implemented the spec would not correctly parse half of the websites online today, because XML empty elements (e.g. <br/>) collide with the SGML SHORTTAG constructs from HTML 2.0+ (e.g. <br// and <p/This is the paragraph content/). But no major browsers ever implemented the SGML minimization features so W3C happily went against their own standard and screwed anyone that did implement it.
It's now 10 years after XHTML became the official W3C recommendation and Internet Explorer still doesn't support it! So we have to do the dirtiest things like serving XHTML with the "text/html" mime type telling all browsers to treat it as SGML-based HTML and not use XML parsing.. which was the whole point of the swap.
Also W3C is back-pedalling now and developing the new HTML 5 spec separately.
So now thanks to web standards, half the web is XML-based HTML but served with the wrong mime type (meaning the browser uses its SGML parser and see lots of syntax errors) and the other half of the web is correctly SGML-based and served with the right content type header. And on top of that almost all website depend on an array of de facto standards and non-standards.. GREAT!
WOOO Go web standards!