Having worked at IBM before, there was a lot of legacy software than ran on PC which would often stop working because of a problem with a remote server. The only way to report such problems would be by calling the help desk. It wouldn't matter whether it was a problem with Windows, or whether you knew exactly what the problem was. It all had to be reported through the help desk.
I imagine that if you use a Mac then it means you don't need to run any of the legacy software. And if you don't need to run the legacy software, there's no reason to ever call the help desk.
I would believe if there were fewer hardware-related help desk calls with the Mac, but I have a hard time believing that PCs require more help desk calls simply because Windows/PCs sucks.