1) So media production is faster at the end of the month? They could just as easily release in the beginning.
2) There is no "enable Lion for download" button. In technology, there aren't "Buttons" for these kind of things. It is a much more detailed and complicated process.
Some common misconceptions. :-/ My intention is not to be harsh on you, but to point out some common flaws in thinking.
Media production is not faster at the end of the month, but the release is done once Apple is satisfied with their GM. With physical copies, they first must decide it is "ready," then begin production of the physical copies, then ship them.
With it being downloadable through the App Store, the minute they decide it is "ready" they can post it to the store and presto.