"Let's say a caster or ranged person steps right up to a guy with a weapon that has reach, can he 'do his thing' without provoking an AoO since without the appropriate feat you can't attack adjacent foes?"
The caster/ranged person won't provoke AOO right next to the guy with reach, but unless he can just appear right next to the guy, the person will provoke an AOO at 10 feet (or whatever distance) while he is moving up to the guy with reach. (The person with reach threatens at the distance of his reach).