What is the point of perimeter rules? At LGA for example, there is a 1,500 mile perimeter. But why does it matter? A 757 taking off for ATL vs SFO is still the same number of passengers, same size plane, same amount of people. What's the point?

This came to my mind when the new DL deal at LGA was announced with US, and I was wondering what DL was going to do with the slots. It seems silly that DL can't build a real hub there for no reason?

Which leads me to my real question. What are the odds that DL and US try to get the perimeters lifted/exempted at LGA/DCA? I would guess it would be more likely at LGA since DL would want to lessen the burden on JFK, but I wouldn't be surprised to see it at DCA, or at least some exemptions.