Apple popularised tablets with iPad. They refined them. Technology got to a point where the iPad experience was a possible and Apple made it happen, importantly with the right OS. Absolutely. But they didn't invent the tablet computer or PDA. There are plenty examples in history of where the leading brand of a product isn't is the originator, and in the field of technology everyone is borrowing ideas left, right and centre. If they didn't, we wouldn't have the progress we have now!
I distinctly remember Archos even had touch internet tablets before the iPad. That's why I find some of Apple's patent claims in the area (basically patents on rectangular touch tablets) so outrageous.
I cant take away from Apple to say iPad and iPhone werent huge leaps though. Really really really huge. I am sure those Archos tablets were complete garbage.