BTW, a regional VW office in Europe looked up my VW from its VIN # and gave me different (higher) tow weights. So I guess it is CYA in the U.S.
Yes, probably some CYA and also some encouragement to buy bigger vehicles offered in North America that just aren't sold in Europe.
But the biggest factor is that European and North American towing practices are completely different.
- tow with a hitch weight
%age that would be considered dangerously low by most North Americans;
- expect to drive at a lower speed when towing (and towing speed limits are enforced);
- expect to drive with greater attention since they are always nearer the limit of stability than North Americans.
So if using a European tow rating in North America, you would have to be willing and able to drive like a European when towing.