You can tow a 4 wheel drive vehicle, including a pick-up truck, with all four wheels on the ground if the transfer case has a neutral position.
And several automatic transmissions in current use allow towing with no modifications at all. They have a lubricating pump that is driven by the driveshaft, so that fluids circulate in the tranny while being towed. That's all it takes.
And some of the cars you see being towed may have been modified with the addition of a transmission lube pump that keeps the tranny lubricated while under tow. Others may have had a drive shaft disconnect added, which accomplishes the same thing as the 4WD Neutral position.
Most standard transmission vehicles are also towable without modifications.
In short, there are a large number of vehicles that are easily towable "four down".
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL