Nokia is known for not keeping promises (e.g. N8) and Elop wants to shake off that reputation, hence the silence. But that's only my speculation.
Incremental availability from a logistic point of view makes perfect sense. But one thing should be clarified - price. If they have any reason for delay the device, price should be the same no matter what, no? So why not announce that? I know that Nokia Finland did, but why not other countries?