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.
RDF isn't as widespread as it could be (it could be used in Facebook and Wikipedia but isn't, for example).
(And I haven't even heard of FOAF.)
I wouldn't call these huge successes.