XHTML hasn't revolutionised web page markup (it brought with it draconian changes {read: made web page markup more XML-like} and is now being replaced by HTML5, which makes some {all?} of its changes irrelevant).
RDF isn't as widespread as it could be (it could be used in Facebook and Wikipedia but isn't, for example).
XHTML has revolutionized page markup. Not because everyone is using it but because it blazed the path for better standards that the other document types follow. Also, many of the changes in XHTML were brought over to HTML5 - which does have an XML definition.
If you're properly serving XHTML 1.1, you're supposed to use the application/xhtml+xml Content-Type, which means browsers are supposed to FAIL to render the page if there are any well-formedness erors.
I guess reality is the best counter argument to your claims. RDF does not exist outside of academic toys and FOAF is so statistically irrelevant that it can easily be said that it never really existed in the first place. As the original article points out, XML may have a place in certain forms of document exchange, but as far as the web is concerned it is mostly just one failure after another.
[EDIT] Don't forget DBpedia and FreeBase (which uses RDF heavily) is used heavily by PowerSet which subsequently was bought by Microsoft which now (as far as I know) is used heavily for Bing.
Freebase wasn't built around RDF - they ended up emitting RDF because it made sense to do so, but the core APIs the service is built on are based around JSON, not RDF.
I don't see how anyone could regard those technologies as huge successes. All three would be in my list of technologies which were overhyped and hugely underdelivered.
XHTML was a failure. Everyone stuck with HTML4 and advantages of XHTML haven't materialised. I question the whole reasoning behind trying to retrofit HTML into XML.
The "semantic web" has never delivered on its promises, despite hanging around like a bad smell. Very few sites use RDF (or FOAF). The real-world problems that RDF was supposed to solve are, in practice, solved by simple JSON-based Web APIs.
The only XML-based web technology to become a success is RSS.
You're kidding, right?