I think it's too harsh to call them "stolen". Apple understood things about these ideas that most others didn't. The end result was something that was qualitatively very different from what preceded them.
As an example, I worked on a tablet in '99 [1]. As the referenced article indicates we were not alone, nor were we first, and more came after. Around the same time there were a number of attempts at gluing together PDA's and phones. With e.g. Palm you had a UI that was not that dissimilar to the iPhone (ironically things like the memory model in PalmOS was inspired by pre-OS X MacOS - it was awful).
But all of these failed to graps fundamental issues that Apple understood, and you have it right when you say they "got to work" on making it work properly, making it user friendly, and so on. But I feel you undervalue how transformative what they did was.
When we started designing the Freepad, it's not like we were not thinking about usability, making it sexy etc. But while I think we did reasonably well in terms of aesthetics, we were too locked into thinking about it as a phone replacement, and letting ourselves be led down the wrong path by being controlled by technical limitations we ran into:
Battery tech had just barely made cellphones viable at that point. Instead of deciding what it would take, and waiting, like Apple did (not just on batteries, but also screen and others), the batteries available at the time dictated that this would not be a device to take out and about. The lack of a well established wifi standard and extremely slow GSM data mean we were led down the route - since battery meant you wouldn't run around anyway - of thinking of this as a home device and consider DECT (wireless home phones) with a data extension as a viable solution, firmly locking you into using the tablet around the house or at best out in the garden.
We ended up with a resistive touch screen because it was the only alternative that was viable cost-wise. RAW and flash was woefully limited, and dictated a model without any app eco-system, because we had to tune everything (hence things like Nano-X [2] mentioned in the article, coupled with our own widget library) to make even basic applications fit.
So while you may say that Apple "just" stole the idea (the idea was not ours either - I grew up with sci-fi describing or showing tablet-like devices; we were never under any illusion that we were first), they did more than "go to work".
What they did was that they refused to accept the limitations, and rather than let the technology-limitations dictate the product and lead them down the path of turning a good idea into a bad one, they didn't compromise and instead waited it out. They did this with the iPhone as well as the iPad.
This is why so many who had seen the previous tablet and smartphone fad reach maximum hype and fade away looked at the iPhone and went "so what?" (I was guilty of that): We'd already had devices that came from a similar idea, and we failed to realise that while the germ of that idea was similar, what we had ended up with last time was an idea that had been compromised in so many different ways that it was no longer the original idea but a corrupted, bastardised version that had lost the important bits when we tried translating it into reality.
I mean, the tablet I worked on was tethered to your house, for example, as mentioned above (and see the title of the article [1] - it references Ericssons "Screen Phone" - which basically says it all: the first generation tablets were either replacements for landline phones - in the case of Ericsson and Screen Media and others - or laptops with swivel screens in the case of PC manufacturers; the latter flawed in entirely different ways).
We didn't start out with that vision, but we let practicalities corrupt our vision, and convinced ourselves that the result would still be good enough, because we didn't see any alternative: It had to be good enough.
Part of the problem was that we failed to grasp which parts of the idea where essential, and which we could compromise on. Mobility was essential, and we compromised on it. Screen quality/touch quality, was essential, and we compromised on it (the screen was great for the time, but awful by the standards of even the first iPad). An application ecosystem was essential, and we compromised on it and never really even thought seriously about it.
The result, to me, is that while the core of the idea might have started out the same, the iPhone and iPad were fundamentally different and innovative from the attempts that went before them, not just because Apple "got to work" but because they understood where you could compromise, and which parts of the idea were essential and had to remain no matter what.
[1] http://www.zdnet.com/article/freepad-norways-alternative-to-...
[2] http://microwindows.org/