I imagine most people will buy a case for this, as this tablet does not come cheap.

When I take my tablet (in a case) out and about, it goes into a laptop sleeve before it goes into a bag. For me, it's not bending I'm worried about, but scratches.

Does it then matter how thin it is if it'll be protected in a bulky case?

It sets the minimum size of the case.

Just attach it to a physical clipboard as you'd do with real paper (joke attempt)

While you joke, I actually used that method on a modified clipboard to hold mine in a zip up folio. I'm super happy with the way it is positioned now because I have it held in place with a clipboard. https://imgur.com/a/thrkIww

The problems with the phone is that it's often carried in pants pockets. I don't think something of this size will have the same kind of forces applied to it.

Actually, I think that things which get thrown into bags on a regular basis face more stresses than a phone in your pocket.

It could be jostling around with corners of large books, laptops, cables, random containers, etc. It can also have more space to accelerate when you swing your bag around, whereas a phone is held firmly your leg when you run/jump/etc.

Durability in a bag is what separates great electronics manufacturers from decent ones. If I buy something and it doesn't survive bag life for several months, which is quite common, then I write off the manufacturer as a creator of fragile throw-away devices. But I've never had a phone have any sort of problem from pocket stresses.

This is much larger than a phone which increases the effects of small bends. I managed to break one of the early large-format ebook readers with a glass display in a jacket pocket, for example.

I happen to have Sony's competing 13" e-paper tablet already and I'd be nervous about putting it into a backpack without something non-bendable next to it to prevent flexing.