I think it's mainly down to the high temps you need for abs. For whatever reason a lot of us start out with abs, so the beds get a real hammer in the expansion and contraction stakes right from the start.
The knp has a 4 mm aluminium plate and that's stayed flat - but it's never been heated beyond 60, mostly it gets used with an unheated bed.

Can you get aluminium bolts/screws ? would be interesting to try 3mm aluminium bed with aluminium fastenings and see if it makes any difference.