Good question - for me it's the surface material which is more protective and easier to clean than the carpet. Similar to carpet
floor mats vs. something more durable such as
weathertech,
tuxmat, etc. etc. If you throw muddy cleats or a dog with muddy paws into the canadian liner, it should be easier to clean than the carpeted version. And I'm not sure how waterproof the carpeted one is, but the "plastic" one definitely is. (It's not a smooth plastic btw, but more of a textured, durable surface - but still easier to clean than carpet)
The option of the more durable and rigid Kia folding tray (or other 3rd party options) is always there, but you lose the easy functionality of the split folding 3rd row to put up/down as you see fit on the fly.
But you are correct - a $170 premium for the Canadian version is not insignificant, so worth considering if you're really benefit from the added level or protection/convenience. There are plenty of pics earlier in this thread which help to show the differences in the surface material.
Finally my personal opinion ... when I received the Canadian liner, I was thinking "For $300 I get this flimsy thing?" .... however after a few weeks of use I am actually quite impressed and glad I paid a bit extra for the protection.