They may have had the app store model planned out from the start for the next version of the iPhone, but didn't want to talk about it when releasing the first version because that would highlight the shortcomings of the existing product and cut into sales. But you still have to have an answer to the question of how you make software for the new product, so they say build web apps.
Rather than saying, "we will have an sdk too, sometime", they played it off as intentional, and continued working on it silently. There is just no way they built it all in the single year from the release of the iphone.
The rest, all the infrastructure needed to have a working app store would be a much more substantial project. It is this part that would be difficult to build in a single year, and would have had to be in the pipeline when Jobs made his statement.