Meh. The whole 'he who must not be named' thing is drawing on the idea in magical thought that by uttering the 'true name' of some evil entity, you somehow gran

Meh. The whole 'he who must not be named' thing is drawing on the idea in magical thought that by uttering the 'true name' of some evil entity, you somehow grant it power. So not mentioning Voldemort by name is a way of denying him that.