Apple's real genius was, as usual, to figure out how to fix other people's broken and half-completed ideas, put it into a pretty box, and market it up the wazoo.
FTFY.
Apple doesn't usually completely think of something out of the blue. However, Apple does think of all the reasons no one wants a product, why the market isn't flocking to something. They get it. Then, they create something that doesn't have any of the issues that caused the previous attempts to fail. As stated in an earlier post, the iPad: No pen, great battery, UI is appropriate and responsible. It just comes naturally to everyone, you don't have to think about using it when you're using it (for most things, anyway).
Perhaps if Palm had been just a little better, if Microsoft had actually designed a proper interface for a tablet, etc. then Apple wouldn't have gained any ground in the markets they're in.
Apple is great at cashing in on all the mistakes their competitors inevitably make due to incompetence, marketing/corporate trying to do the designing and/or insisting on sub-par component suppliers. Stop making mistakes and you'll stop Apple.