I don't think either Microsoft or Apple software is particularly "user friendly". And certainly not more than most open source software. I think it's just a) familiar (to people who use it), and it's b) incessantly marketed that way.
At best, some of the software on each platform has some superficial visual similarity which I guess is like friendliness, but ultimately, I think it creates an expectation of consistency on which it usually fails to deliver.
@lightweight Apple took the right approach to user friendliness; hide from the user the technical workings of a computer. This however made the Apple UI unacceptable to users who want to explore the technical workings.
Windows has always been user unfriendly, but it was shoved down our throats.
