Keep it stupid
I think people working on digital interfaces are the only ones to be challenged to make a product usable even for people who has no clue what are they doing.
Designers are encouraged to build a complex interface for an online service that should be intuitive and usable by someone who don’t know what internet is.
You put the perfect example with ipod’s wheel. If you take an ipod for the first time and are not told how to use it there is no chance that you will figure out that the circle is touchable and it’s meant to be used as a wheel. Because wheels move, and it doesn’t.
We are told, even by naming it wheel, how we are suposed to use it. But it’s not intuitive. How to use it is not inborn knowledge. And still is easy to learn how it works.
Interfaces are not magic and always need some learning. What we sure should include are assistance, so users never feel cluelessly stuck at any point, and make them accessible — because most aren’t.