My whole interpretation on Black City & White Forest is based on the theory that the Black and White version differences are the result of a split time-line/alternate universe.
As you know, a long time before the events of the games, the two kings of Unova went to war with each other, both aided by one of the Legendary Dragon Pokémon. The split in the time-line lies in which one of these kings won this war, and thus went down in legend as the hero with a Dragon Pokémon.
So, the events of Pokémon Black are the result of the King with Zekrom winning the war. Under his rule, the Unova Region embraced technology, thus resulting in Black City being built where White Forest would be.
Conversely, the events of Pokémon White are the opposite. In this version of the time-line, the king with Reshiram won the war instead, and under his rule, the Unovan people we're taught to respect nature, which is why White Forest is left untouched as national parkland.
The other version differences (Iris/Drayden, version exclusive Pokémon) are the result of the split timeline having many other smaller effects.
Does this all make sense?