What you say makes no sense. Tablets are independent computers. You don't have to be connected to the internet to make the most of it. You rely on these internet services only if you choose to. I can read a book, listen to music or watch a video without Pandora, Netflix and Co. A tablet is not a dumb terminal.
Unless your talking about taking photos / video from it, but that's another story as a cassette deck can also record and play back audio without being a computer.
Granted, you can play games with one or write notes etc, but I just mean they are mostly used as connected devices.
And that's true for any desktop or laptop as well. It doesn't make them dumb terminals either.
It's possible you could jury-rig something up for a tablet, but it's also clear the intended use is as a networked device.
Because phones and tablets don't have SD slots? or data transfer from blue tooth or NAS drives isn't a thing?
PS: iPhones and iPads don't have SD slots so for millions of these devices that do qualify as phones and tables it's really not an option.
That doesn't help making the differentiation between a terminal and a standalone computer. Computing has always been a networked thing, we just now have a transport medium that is faster than a floppy disk.
Mainframes were loading punched cards, cloud datacenters are loading user data, and tablets are loading books and video.
And the moment you annotate that PDF or manage synced documents, you are now editing content.
At least in the context that a modern PC's graphics card is not thought of as a separate computer.