I'm not the techie guy here or anything, but I think Michael said that it was a vBulletin 3.0 vs 3.5 thing. ENWorld runs on 3.0, while NTL, NKL, and CM runs on 3.5.
Upgrading to 3.5 is problematic, because ENWorld's code has been hacked to Baator and back, in large part by people who don't work on it anymore and didn't leave much in the way of documentation regarding what, exactly, their hacks do.