I think that by choosing Mitchell and Webb's Peep Show-esque characters Apple have made a brave decision:
Mark Corrigan/David Mitchell/"PC"
In Peep Show, David Mitchell plays the hard-working, dependable Mark Corrigan. OK, so Mark can be pompous at times, looking down on his unemployed flatmate Jez, but he is always there when you need him and he doesn't let you down. Sure, he is slightly flabby around the middle and slow to embrace new trends, but he is a predictable old friend who can be depended upon when the real hard work needs doing. And yes, we don't like to mention his occasional nervous breakdowns, because they never last long and he's soon back on his feet doing the jobs that need doing. It would also be unfair to say that he isn't any fun: he likes music and movies as much as Jez, it is just that he doesn't get carried away and let it affect his work.
Good old dependable Mark. Good old dependable PC.
Jeremy "Jez" Usborne/Robert Webb/"Mac"
Robert Webb's Peep Show character is Jeremy Usborne. Jeremy like to be known by the annoying nickname "Jez". Jez is a fun guy with loads of cool friends. He is always partying and pities his flat mate Mark who seems to spend all his time working. But secretly Jez feels empty inside. His life doesn't seem to have any real meaning. He is sure he looks good and people often seem impressed with his ability to have fun. But Jez worries that he isn't capable of hard, meaningful, productive work like Mark. Sure he makes the odd bit of music, but where is his life going? What is his reason for existing?
Poor, shallow, pointless Jeremy (sorry, I mean "Jez"). Poor, shallow, pointless Macintosh (sorry, I mean "Mac").