The extra field for name in threads is not the same as Display Name in UBB, it's just a way of letting users give out their real name if they want to. It's not used anywhere else than on the profile listing as far as I can remember and it is not in any way a required field.
It's up to everyone to decide for themselves if that is good or bad thing, although I realise that it is a hassle when switching from UBB.
