Yes, FeedBurner does this[1], and we do it too with Full-Text RSS[2]. The feeds should render as a regular webpage in your browser, but if you view source on those feed URLs, you'll see regular RSS output (XML), but they both contain XSL to transform the XML to HTML in the browser:

FeedBurner:

    <?xml-stylesheet type="text/xsl" media="screen" href="/~d/styles/rss2full.xsl"?>

Full-Text RSS:

   <?xml-stylesheet type="text/xsl" href="css/feed-free.xsl"?>

For anyone attempting this, note that there's an escaping issue on some browsers that requires Javascript to fix[3].

[1] http://feeds.feedburner.com/johnpilger?format=xml

[2] http://ftr.fivefilters.net/makefulltextfeed.php?url=http%3A%...

[3] https://bugzilla.mozilla.org/show_bug.cgi?id=98168#c80