It's the expansion pack so it's customary to have a separate entry. It adds a whole new faction as well, from 3 to 4 among other things. Much more than just a few tweaks.
Played a bit this weekend with LOUD, living it up! Great times when there's not a massive amount of lag (I remember painful 4 hour games with my best friend) but the AI set to 1.2-1.5 is a killer, I'm way out of practice with it.
It's just a new release of the same game with a few tweaks