I somehow doubt this. I'll guess it was just a good place to cut off rest of the map. It also is a lot better than straight invisible walls like in Fallout 3, imo. Feels more natural that way.
But I wouldn't have anything against it, if DLCs would add / fix / change stuff in the game world, without adding some new places where you have to travel to. There are still enough places in New Vegas, where locations could be more flashed out. As example, all these locations where few npcs are running around and only one has a limited dialogue. Locations like west side militia or aerotech office park, etc.