Amiga and 68k MacOS is intuitive. I've seen people who have never used a computer before get the hang of it in around a minute. My cousin who is actually quite thick had no trouble remembering amigados commands and any other tinkering, but gave up on computers (meaning PC) when the playstation 2 came out.
I found Windows 95 simple enough to pick up after only knowing how to use a dos based directory manager.
Use to be that you could learn the basics without ever consulting a book or guide.
My theory is this:
Some people "get" computers. They can find their way around most systems without too much fuss.
Some people don't "get" it. They can memorize how to use specific systems and where to click on a specific screen, but they'll always need help or new directions even for a slight change.
Some people of course may "get" everything but a given system, and some may never "get" it except for a given system that just somehow makes sense to them.