I've owned several Rangers, and while they are not tops when it comes to handling, I've never rolled one. I would say it's safe to assume that any vehicle can rollover given the right circumstances. If they made the Ranger rollover proof, I don't suppose any of us here would want one, picture it wider and lower, severely lacking ground clearance. If you want a vehicle that is least likely to roll over, buy a car. The general nature of most trucks make them more prone to rollover or at least poorer handling carracteristics than a passenger car.
If anyone here has ever driven an older pickup, and when I say older I mean pre 1959 or so, particulally the first pickups. They were trucks, no shocks on most, straight axles, most with straight 6cyl. engines that were built to do work, they weren't used as daily transportation or as grocery go getters. Even a heater was optional and somewhat rare on some. Those trucks were slow, hard to drive, and handled about like a barge on the highway. But yet we didn't here about rollovers or crash ratings.
I don't disagree that times have changed and modern tech has made things more reliable and safer, but we have to keep in mind that these are still trucks.
One vehicle that was known for it's rollover concerns was the Jeep CJ5, but yet I drove one for 8 years without incident, while yet a budy of mine had trouble keeping his right side up. I went the same places as he did, drove the same amount of off and on road, and never flipped mine. As with anything else, it's a matter of knowing the limits of your ride, if you buy a 4x4 Ranger and expect it to handle like a sports car, then you will most likely end up on your roof, but if driven with it's design and handling characteristics in mind, then you'll be fine. One way to look at it is to never drive harder or faster than your brakes will allow, and you will always remain in control.
I've seen way too many accidents where people loose control of a vehicle trying to avoid an accident only because they panicked an were simply going too fast for their situtation or simply not paying attention. If you don't let yourself get into a panic situtation by tailgating or speeding, you are far less likely to loose conrol, rollover or crash.
When I drive, especially on the highway, I basically assume that the other driver can't see me and doesn't know how to drive.
While I am sure I could roll my 2 wheel drive if I tried, it's far from being top heavy, and I've had early Explorers and Ranger 4x4's and never had one even close to going over on the road.