I’ll tell you something else: web browsers will handle the macroformatted example just fine. I’ve been using this technique on Cafe au Lait and Cafe con Leche for years and it causes exactly zero problems. All web browsers back to Mosaic 1.0 simply drop out tags they don’t recognize. Feel free to sprinkle as much XML tag spice into your documents as you like. You won’t cause any problems for browsers. They’ll just render the HTML as usual. More modern browsers (pretty much everything since IE 5) even allow you to key off the new tags in CSS or, even more powerful, XSLT.
The only reason I can imagine you might choose a microformat over a macroformat is because macroformats are invalid XHTML, but so what? XML doesn’t have to be valid! That’s a deliberate design decision in XML. Some say invalidity is the real revolution in XML. It’s what XML brings to the table that SGML never had.