The beauty of Genshi is that its templates are pure clean valid standard XML, so it interoperates perfectly with all XML tools, and it has independent serializers for all the dirty quirky variants of HTML. So you can render your templates in XHTML, or any other version of HTML you want, and edit and process templates with off-the-shelf XML tools, that don't need to know about any special non-standard syntax.

Templating languages that use almost-but-not-quite-entirely-unlike-XML or -HTML don't work well with standard XML and HTML tools, because they don't recognize XML-or-HTML-with-some-magic-non-standard-syntax-sombody-nailed-on-to-the-side.