I remember that system back in phantasy star online where rare drops your character could get was tied to a character specific variable determined by your race, name and choice of physical features. If you didn't have the specific combination on your character, you couldn't get the specific item.
There is no way to know wether a similar system is at work in wow, but given they already had to fix something having to do with too many legendaries dropping for some characters (this is a fact, there is insight about this in one patch note), something similar might be at work.