To be able to give a solid release date from every retail outlet, Nokia would have to say nothing about plans and intentions and not give a glimmer of information until everything is ready and they were almost shipping from the factory.
Then they would have to give retailers strict instructions to not sell stock until some artificial and planned release date that is suitably late to account for unpredicatble delays in shipping and importing.

In this case the initial announcement would have been about Nov 7th-8th.pf a release date of, say, Nov 27th. Many retailers would have them on the 16th but not allow anyone to buy them until Nokia's conservative release date is reached. That is how other manufacturers do it and that actually results in the device being in your hands at a later date.

Nokia's current release tactic is to get them to the retailers as quick as possible and allow them to ship them to customers as quick as possible.

What would you rather, a definate date of November 27th or the vagueness of 'as soon as your retailer gets them'?

The N900 is an open device, the pre final build announcement is a courtesy to the community to allow developers to hit the ground running without using restrictive NDAs.

It's a difficult and painful process but, in the long run results in a better device quicker at the expense of a rock-solid release date. I thank Nokia for doing it this way.