Apple has had a policy for a while now that basically says that you cannot merge multiple Apple IDs. This is becoming a problem as various change this year have caused problems with users needing to log in with each ID. Back in July TUAW said:
Some readers have been managing two Apple IDs on purpose and are now frustrated about the fact that Apple is restricting logins for automatic downloads. Others have only just discovered that they have two IDs. Most of them have already contacted Apple, only to be given the same answer without exception: Apple will not consolidate Apple ID accounts.