I think that's all because Apple soon launch new "cloud" service with joining MobileMe and iTunes. This thing forced Apple to sign a new agreements with Music Labels - i think they requested Apple to clean up and provide them info of all their client base - because this new cloud service allow you to stream your music on different devices - you know how Music labels paranoid about this.
By the way Google yesterday already launched in Beta the same cloud music service. Apple will be next.
So i think that new restriction just checking your address with phone book - it must be correct and match.
All this crap about credit cards are stupid - Apple can't check your credit card address if you have made account by gift card in first place and never enter any CC info to your account. So it must match phone book address.