Post-PC devices are not necessarily keyboardless tablets. The transition we'll see has much more to do with where the data is stored and where programs are running than with the physical format of the device.
Then it needs a different name, right? "Post-PC device" implies it has left the PC model behind, and although new input methods may arrive, PC's will still be around. Specifically, laptops are what I'm thinking of when I say PC, and the even though the form factor isn't evolving rapidly, tablets have been around a long time and the form factor hasn't evolved that much.
Now, maybe you'd say that the shape of an iPad is way different from the shape of a windows table from a decade ago, but it isn't. They're both as flat as possible with just a screen.
The transition to SaaS and the cloud does not mark the end of the laptop.
Your idea of personal computer is something with a keyboard or the device physical form. I interpret it as something much more related to function - a device that holds and processes data locally, with locally installed applications and that you have to manage yourself, dealing with files that can be processed by different applications. This has been what a personal computer is since their invention. A "post-PC" device (and I see it as mostly a marketing term, but a useful way to refer to these devices nevertheless) is something that won't make you manage your files, that has a simple way to install/remove applications and that is tied to always-available remote storage and services. A Chromebook is much more post-PC-ish than an iPad, but that's another discussion.
