Here is an example of a URI using client-side XSLT in the library of congress. They are definitely using this feature.

https://www.loc.gov/standards/mets/profiles/00000016.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <?xml-stylesheet type="text/xsl" href="echoProfile2html.xsl" ?>

Before calling people arrogant you should validate your own arrogance.