The thing that would determine this is whether Amex paid a fair market rate for this access. Could Chase come along and offer the same price or slightly more and also get its card holders the same access? Then it's not a cornered market. But if Amex is getting some sort of preferential treatment (even if it's illegal) then I think you could count it.
About examples of a cornered in the Credit Card, could it be “with a Black Master Card you can enter the VIP lounges in the airports”?
The thing that would determine this is whether Amex paid a fair market rate for this access. Could Chase come along and offer the same price or slightly more and also get its card holders the same access? Then it's not a cornered market. But if Amex is getting some sort of preferential treatment (even if it's illegal) then I think you could count it.