Some people put leveling kits on them. I didn't, and I doubt I ever will. My F350 is much higher in the back than the front when unloaded. With my trailer on it's about level.
My friend's F250 looks a lot more level than my truck. I measured once and mine is the same height as his in the front but 2" higher in the back. Mine does have a slightly heavier suspension option (11,500# GVW package), which may account for some of that.
I'm not sure if what you're seeing is the result of heavier suspension or a leveling kit, but some trucks definitely sit more level than others.