I'm sure, internally, GameStop Corperate has crunched the numbers and they know what they're doing... but it just seems silly. Even if the third store within the mall is profitable, it seems like it'd just be cannibalizing the sales from the other two stores. Meanwhile, you have to pay another set of crew members and what's generally crazy-expensive mall rental fees.
Basically, what I'm saying, is that I doubt the third store is making enough additional income over what the first two stores would make by themselves to justify the additional charges (rent, payroll, etc...).