I've had 4X4 pickups since the late 70's. I've never been without at least one 4X4 since then. I will have to say that, although I know we are talking about an RTV, my Yamaha Rhino will go so many places a 4X4 pickup won't that I can't even begin listing all the places. In swampy areas one of the biggest issues is weight, a 4X4 truck will be sunk and buried where I can get through in 2 wheel drive in the Rhino. Even with the most aggressive tires on a 4X4 pickup, it won't go up half the hills the Rhino will. The twisting, turning trails I have with plenty of hidden sink holes would be impossible for a 4X4 pickup. This is all besides the fact that if I do by chance get stuck on my UV, I can go out and drive a steel fence post in the ground, and winch myself out. This wouldn't be an option with a pickup. Also, the Yamaha Rhino will climb hills that even the most experienced ATV riders have simply passed on trying.
I currently have 3 4X4 vehicles; 2 pickups and 1 SUV. Both pickups have lift kits and aggressive off road tires. One pickup not only has the locking differential in the rear, but has an air locker in the front. It will go where most 4X4 pickups don't dare. However, if you even remotely think that a pickup will go where a Rhino will go, you obviously have never driven one. The RTV does fairly well, but does not have the power to keep the tires cleaned in really deep mud and does not have the power to climb really steep hills. Still, I don't think you can even make it in a heavily modified 4X4 pickup where even the RTV will go.