I remember when the WIMP GUI was so new that everyone had to be trained in it. Now older users have been trained and younger users have been brought up with it, so it seems natural. If you did the same thing with a decent command line, you'd end up with every moderately educated person being a wizard on the command line too. Put another way, computers didn't become popular because of Windows but because of DOS. The Mac, despite its "for the rest of us" tagline and mature GUI way before Microsoft's offering, wasn't the machine everyone ended up buying.
I used to think that computers needed some natural UI. One of my earlier academic projects in the '90s involved all the bullshit with the spinning 3D objects which you could open/close/put under/otherwise manipulate, and I thought I was so clever. Now I'm seeing this sort of thing attempt to reach mainsteam and actually look quite fluid, and I think the same thing now as I concluded back then: it's not worth a miniscule reduction in learning curve to be so restricted and drowned by eye candy. Contrary to popular belief, most people have wonderful brains which can accept new instruction and traning to a good old age. All they have to do is think and concentrate a little, and they'd be much better off with a powerful interface rather than a "natural" interface.
Of course there's a balance, and nothing inordinately hard to learn will ever reach mainstream. But look to a few hundred years ago and even reading and writing was regarded as something that only the elite could do. Yet at some point we managed to unify the planet on the notion that being able to read and write is a reasonable goal for everyone without serious physical or mental difficulties. Why must we dumb things down again?