well, i know on my neuspped race springs that the springs are only under compression when the wheels are on the ground. the rebound of the spring isn't long enough for them to be under compression when the spring/strut assembly is removed. it's that simple. when they're on the car they're as compressed as any other spring, but when they're off the car the weight of the car isn't compressing them. so the springs are not compressed.

like dantastic said. if the springs aren't compressed you don't need a spring compressor. let's use a little common sense guys.