You have a much wider range of pokemon in B2/W2 too. Before the first gym you can get 12 different pokemon. 13, if you include your starter. Also quite a good range of types. Water/Electric/Grass/Flying/Dark/Fighting/Bug,Normal.
I'm very impressed with what was added into B2/W2. The habitat dex is one of the best tools I've used. Will be deeply disappointed if it isn't in X/Y
Though it appears you can catch Pokemon in multiple generations in X and Y, we actually don't know for sure. The designers often show wild Pokemon in early screen shots that you can't really find wild.
Though with Sylveon in the mix, we should be able to get Eevee, may I remind you about Tangela's availability in Diamond and Pearl; ie. nonexistent?
Creator of Jay's Journey (see quote!) "It's not ten years old! Therefore, it sucks!" - Nostalgia whores everywhere