I think the main reason is/was to not get them stuck so much. Might be that yours actually works better with the new landscape, though. Imo one of these "test and see if works" topics. ;)

> What are the arguments to the contrary?

It's not so easy to do technically. Vertices only determine collision with the landscape, not collision with other objects. What would be needed is a so called "solid mask", but this would then let everything collide with it (technically it makes it part of the landscape). So Clonks couldn't stand in front of material chunks anymore, but would need to climb them. I would imagine this can be quite annoying, and also Clonks could get stuck when a chunk of coal or something falls on them.