What is telling is that for as long as we've had the familiar "full UI" of a "real desktop", many intelligent and motivated people still struggle with many of the conventions. Have you ever marveled at the fact that most desktop software in 2010 still defaults to destroying your work? And if you do want to keep your work, it insists that you give it a name, a name which must be unique and must not contain certain characters that the computer is entirely capable of understanding, and then it asks that you choose where in some invisible hierarchy you want to keep it (even though the answer in almost every case is is "where I can find it again"). All of this complicates something that might as well be done with pen and paper.
These are things that everyone who uses a desktop interface has to get used to, and there are some good reasons that they are the way they are, but they aren't necessary things for the task. It is possible to safely shed all of these conventions and end up with something that still gets the job done, possibly better than the traditional desktop way.
Computers can be very powerful tools, but I am not sure many people are really interested in using that power -- I think many, even those who grew up with computers, would like the details to go away.
To follow your car analogy, cars used to be much more complicated to operate than they are now. Modern cars have electric starters, automatic chokes, and in many cases automatic transmissions, for instance.
Apple is simplifying things with iPad, Google is heading in the same route with Chrome OS, and I'm sure there are many other players we haven't heard from yet. It's going to be very interesting how things eventually play out.
Computer usage is more like math. It's something you just need, part of every day life, though many people still hate it, as it is more flexible. GUI's really share similar concepts, you just have to adapt them, and if people hate one word, than it's adapt - seriously hate.
You really have time to figure out how things work and GUI's are really no rocket science to figure out.
Nobody expects users to become system administrators or application developers, but answering questions about self explaining clickable graphical elements is very painful. (With a little endurance you could probably get a chimpanzee to understand most of our 'modern' UI's).
What is realy apsent from the mind of older generations is the idea that computers are just tools, albeit imensly powerfull ones, and as with all tools we need time and especially motivation to learn how to use them.
Personally, I don't give a damm how my car works but I had to learn how to use it to get form one place to another and it would certainly be much harder to do it if every other car had a radically diferent set of controlls.