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.
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.