This works wonders with most CSR's. If one is polite and generally a decent human being towards the CSR, they will generally do what they can to help someone out. To be honest, they're usually dumbstruck when I ask them how they're doing today. If they aren't polite and helpful to me, I thank them, hang up, and call again to get a different CSR.Nice one OP!
I think this is as much a lesson in being honest and nice when dealing with retail workers, especially during the holidays. My guess is that the Genius Bar is authorized to do that on a judgement call basis, and you were nice and didn't yell at them so they did you a solid. I'm sure they get a lot more bitchy people than nice ones this time of year, and I know when I worked retail I would go out of my way to discount things for nice people over the mean ones.