They do vary. Each carrier has their own policies.
You are correct, sir.
It's hard for me to say with any certainty. I only know, for sure, of three (Panther, FedEx, Express-1). I would imagine that the larger (and/or the older) a carrier is, the more likely they are to have such policies in place. It depends on their experiences with cargo vans running long distances (accidents, late deliveries because the driver had to sleep, etc.) and on their ability to swap loads out to other vehicles in their fleet (availability of vehicles and availability of cross-dock locations).
Long before the buyout, Con-Way NOW had a policy for cargo vans. Con-Way NOW's policy was 750 miles, IIRC, but it was not a hard and fast rule. It was always "roughly" or "about", and there were many cases where much longer loads were allowed to go straight through. At Panther they had a policy that was equally not a hard and fast rule, right up until they had a couple of instances where near the end of long runs drivers got into accidents and fatalities were involved. The ensuing lawsuits resulted in much more rigidity in the rules.
I think I've more or less answered that above, but the reasoning for limiting them is obvious, for safety, and I think the reasoning for not limiting them is as stated above, having no or very few bad experiences, and a lack of available vehicles and swap locations to Pony Express the freight over long distances. The more responsible drivers know their limitations and will more or less self-regulate themselves without having the carrier to impose the regulations. Smaller carriers can have a better gauge on which drivers are responsible and safe, and can more easily tailor loads to those drivers. The larger the carrier, the less likely the carrier is to be able to, or make the effort to differentiate between responsible and irresponsible drivers, so they create rules to cover all possibilities and to limit the risk.
