I always assumed it was just a combination of regulatory body idiocy and caution on the side of car manufaturers. So I didn't feel bad putting a hitch on my diesel Jetta and towing a trailer with it because it was rated for at least 2500 lbs in Europe.

But a friend who is more auto-literate looked into it and said in Europe the way trailers are positioned is different somehow such that the weight on the hitch is different.

Also more aggressive speed limits on trailers and other safety regulations enforced on the drivers.

So I don't know, it might actually be partially legitimate.