HaLeivi: It is clearly stated in gemara and shuchan aruch that you should whisper loudly enough to hear yourself or you are not yotze. We do not pasken like that zohar.
wellmeaning: It is a derivative of the vernacular, and the differences in how they speak it are the differences in the vernacular of those places. At the same time they are also the differences in how they speak Hebrew, proving where the variations come from.