The HTML email world is stuck with HTML 4.1, inline CSS and many corner cases (worse than the IE6 era!).
It might be for the better, actually. HTML5 and CSS3 are Turing-complete so I can imagine that the moment they would be allowed, some clever marketing company would figure out new and impressive ways to use the new features to scam people. Er. I meant, "provide value-added content".
 - with user closing the loop, see http://beza1e1.tuxen.de/articles/accidentally_turing_complet... for links to an example.
You can do worse with less.
It doesn't belong on that page.
(Hint: basic arithmetic is turing complete if you give it the same affordances)