It's not just the employees - if you provide a service that your customers depend on to provide their service, they're not going to appreciate the hassle on a holiday especially when it's not at all their fault. This isn't true so much for GitHub, but is for infrastructure providers like AWS.
Tell that to rackspace not sure how many where effected on Christmas Day they decided to update a router - causing a 3-1/2 hr outage from 8:30 est to 11:00est aprox, took out part of my infrastructure - made for a nice Christmas morning surprise. Effected the ORD datacenter- only thing I could on RS status is https://status.rackspace.com/index/viewincidents?group=2&.... And of course the ticket in my account
