I actually just touched on this in another thread here...
Actually, I had left HTML enabled on purpose to ease the transition to vBulletin. As you may now have noticed, older threads that used the QUOTE and URL and IMG and other UBB tags didn't exactly weather the import very well. The import mechanism actually took the code and HTML-ified it. I was planning on leaving HTML display on for a couple weeks while those older threads and posts would drop away, but now that people know that it's enabled, it's time to shut it back off.
HTML has always been off in the past on AppleInsider. The reason you are seeing some HTML code pop up in some threads is because of the way vB imported the old UBB threads, as I mentioned above. Only old threads are affected by this "bug". New threads and new posts won't have weird HTML code popping up in them unless people are actually typing HTML into the body of their messages.