well, it's not exactly lazy programming.  the wiki system they're using is the most popular wiki system out there by far, and it was made years and years ago when they decided the best way to deal with security and regular users (not people who knew how to hand code)  was to use pseudo-code. javascript wasn't as advanced as a language, i think, and i know the practice of clean DOM scripting wasn't in place.  unless i'm remembering wrong, there were no rich HTML editors for textareas yet.   iirc, the most i saw at the time in terms of javascript and forms was a little bit of input validation.  so pseudo code enabled people to add HTML properties without having to know HTML.  phpBB uses pseudo code, too, so much rich editing online was done that that way.

things have changed and advanced, and there are both free and commercial JS modules that can duplicate a full HTML editor.  but there's a huge community around that wiki system now.  it's the backend  for the entire Wiki Media line, for instance.  almost everyone who uses wikis at all are used to using this system.  so even if most of the Web is doing something different, most of the people on it who post to wikis are still used to this system and its pseudo code.

that said, my guess is it's possible to implement some JS rich HTML editing on the client-side and keep the backend mostly the same.  but it would be a lot of trouble to work against usability norms, which is generally a bad idea and has its major drawbacks in the best of situations.