I'm sorry but I don't believe it.
My store has 66 preorders (We actually have more Xbone reserves)
We are a town with 1 gamestop in the 15 mile area, a town of 30,000 with several smaller towns nearby where we are the closest gamestop.
In a town of 100,000 you probably have at least 2 gamestops if not more to supply units to. I don't believe for a second that one store was allocated 600 units for preorder. There simply is not enough square footage in an average gamestop to store 600 consoles (And that is just PS4, not to mention XBONE, 360, PS3, Wii, Wii U and Preowned consoles, and Holiday shipments)
I can answer you right now why he told you 600 on the phone...Because he wants the consoles out of the store (And out of his stockroom), he told you a higher number to give you an idea of the kind of demand surrounding them to incentivize you to pick up your order day one.
I've heard it so many times where employees tell whatever lie they can to either get you off the phone or pick up your reserve or whatever... It also could have been a new employee who knows absolutely dick about the numbers and just made up a number...
I'm not saying there isn't that kind of demand, but the supply and space just simply aren't there.