I don't think OS X nor iOS are much easier to use than their free counterparts, it's just that new users have at least two incentives to learn them, and so they do, without thinking too much about it.

First, they have a positive reinforcement: Mac is "hip", so you'll look cool by using their products (the fact that everybody and their mother owns one or ten doesn't seem to diminish this perception), and also a negative reinforcement because everybody knows "Apple makes easy-to-use products" so if you don't learn to use them quickly you'll look bad.

I'm sure Linux and *BSD have earned more followers by looking different or difficult than by trying to be "easy" (whatever that word means). But that's a discussion for another day...