Well... Think of it as a natural progression.
First movie's titled Batman Begins cause the franchise's starting over. And they're exploring the character's origins. So it make sense.
Second movie's titled The Dark Knight. Now Bruce has had some time to start to grow into the role of caped crusader. It starts getting a bit more personal as he faces off against his true opposite/foil.
The third movie would probably get a title that makes sense.
What I find utterly ridiculous is the stupid secret code name they gave the movie when refering to it on set.
Regarding Harvey Dent/Two-Face... I recommend you read through the articles at
www.filmforce.com on the movie's development.
As far as I take it, Harvey will be in this movie and it'll be Harvey. They're being purposefully vague on Two-Face cause they don't want to overload the movie. And I think that's a good idea, as Two-Face can then be the main focus of a third movie, maybe even get Catwoman in that third movie too.
Hope this helps.