Not necessary. If you had the source code to FaceBook, most likely you won't be able to do much of it.
The one who is focused on running a business on it - yes, would make a lot of it. Irrespective of who else has the raw code.
That's true, but the whole idea was to enter a market with very little to no competition. You would have the advantage with being unique. However, entering a market with 12 other people with the exact same product wouldn't be ideal.