Everyone and their mother has a pickup truck around here... apparently there's almost 5M pickups in California state for a population of about 40M people. Lots of pickups. You often see two pickup trucks in a house's driveway, not counting large SUVs.
American pickup trucks are they way they are because of American travel distances and roads. Our roads tend to be fairly wide (two lane roads are almost always at least 6m wide unless you're in very rarely traveled areas) with gentle curves; Americans think little of driving an hour to get to a job site - and in many parts of the country, 500km trips are regular and 1000km trips not unheard of. As a result, pickups tend to be pretty wide (~2m wide) and long, spacious and comfortable.
Cabover (COE) trucks are entirely a "medium duty" to "heavy duty" thing - there are no American pickups which are COE (Jeep had a "forward control" until 1965), because Americans don't need a shorter vehicle that has an "inferior" ride.
American pickup trucks come with very powerful engines. Typically even the smallest engine offered is more than sufficient for most actual "pickup truck" needs; the lowest output engine that the F-150 is offered with gives this large pickup truck acceleration which would be respectable in the sports car class 40 years ago, and considerably higher output engines are available, though they increase in complexity and fuel consumption and often put the pickup truck solidly into the "medium duty" range of things with GVWR up to 8800kg.
What to look out for? Assuming you're looking at a used vehicle, look out for the same issues as any other used vehicle. A pickup is just another shape of car, really. You can look for signs of overloading by closely inspecting the frame, but in all likelihood unless the truck has been seriously abused you won't see problems there before they're severe.