I was talking more in general terms of cnc machines, a metal or even a wood router/mill cnc machine should not use IGUS rails, but a low weight 3D printer or a laser, could and can use the IGUS rails with good results.
I have however, not been able to do any long term tests of this kind of system yet. As I've recently just started testing the IGUS rails out on a custom designed 3d printer made up out of alu, carbon fiber and both IGUS rails and roller wheels in v-slotted extrusions. The design also welcomes the HWIN rails, so if my testing shows that I can't use the IGUS system, I will just move to the HIWIN system.
The design was just a mockup of a placement idea I had, and was constructed while I had some time of at work. No real design thought beyond the general placement was considered.
And I agree with you, that pre-loaded profile linear rail system is a better option. It was just to add an option of something someone might think of, and having it in here with both pro's and con's. Which would allow them to decide to choose a similar, or different design. If it would fit most of their requirements, not only in the machine, but also in their pocket.