OSX 10.1 will be available at the AppleExpo, exactly one year after the PBeta. This Expo is the most important computer show in France (more than the PC expo) and is an important expo in Europe. And there is the Seybold show, on the American side.
These shows are the moments to debut intensive marketing operations (we are still waiting for them).
And remember, Apple takes about 3 weeks to put the OSX on the shelves of computer stores after a GM is declared (that was true with PB and 10.0).
So the end of the month is the most probable date.
Another thing : according to reports, the Airport management software seems to be in the builds, and is working. The DVD player is still not usable, and until is it not, Apple should wait. It would be more satisfying for the user to download a finished software on the 26th of september than having a unusable player on a CD at the same date !