I wonder about this all of the time because I can see a lot of things about my environment as a child that could be responsible for my own perfectionism (lack of challenge, constant undeserved praise from parents and teachers, etc.), and yet even without those things in his environment, my son is a perfectionist as well.
Lately, I've been wondering if it isn't a fundamental difference in the way gifted people see the world that makes so many of them perfectionists. I suspect that they're often comparing the real, material world to some abstract, ideal parallel reality--something along the lines of Plato's Forms or ideal states (Plato must have been the ultimate perfectionist!). I think heightened awareness of and preoccupation with how reality diverges from some abstract ideal manifests itself as perfectionism and also drives a lot of gifted people towards public interest work and truth and justice causes.
