Did you read the letter at all? It's pretty clear that this has been the plan all along, it's just taking them time.
What they DID realize is that people can't be patient if they don't know what's coming. Not saying this sooner was a mistke.
Steve SHOULD have said this back when they told developers to make web-apps. You know "we'll have an SDK in 2008, but to tide you over until then, you can make web-apps."
That would have made everyone a lot happier, I think, even though it's no different from what we got.