No. Corporations should not have the ability to arbitrarily discriminate against anyone, especially not their own customers.
Also, Apple is a commercial entity which sells custom boutique computers, their customers have no other source to turn to for repairs. You could maybe make a case for them being able to decline (for what valid reason, seriously?) if people could just go to a mom and pop corner PC repair shop to get the job done there, but that's not really a realistic alternative now is it? Not when the whole $5000 computer is glued shut and every single part in it short of the CPU and memory sticks are proprietary.
They aren't being arbitrary. They set some rules, he knew the rules, and he broke the rules.