It's not that ironic; it's a web page that contains far more information that one might expect in any but the largest of emails.

The web is where the eyeballs are and nobody's going to convince anyone of a new idea by wrapping whole-page content in a <pre> tag, no matter the idealological purity this would reveal. To reduce friction (already created by telling someone to potentially change email clients) with readers the author needs to speak the visual language of the medium.