Actually, The map is slightly changed. It's not just a new skin. The removed the ramp up to the inhib and improved placement of the spawning pool, shopkeeper, and the laser turret. Probably tweaked turret locations a bit as well for map balance.
EDIT: Also, if you've seen any over the work in progress pictures, they built the map from the ground up. To me that all equals a new map, even if it is based on a current one.