Much like what was recently done for Operation Flashpoint. Instead of calling it Operation Flashpoint 2 it's called Operation Flashpoint: Dragon Rising, and it's largely because the original was so long ago a lot of people won't remember it.
I'm pretty sure Operation Flashpoint dropped the number '2' because although Codemasters had the rights to the name, they didn't have the rights to make the sequel. (It's a great game by the way, I'm really enjoying it at the moment).
But I agree with you, dropping the numbers is a good thing. Star Wars (original trilogy), Indiana Jones, James Bond, all good examples.