[B]Because, this is what Apple does. Do you think that their products are somehow magically ready the day of an event, and not before?
"This is what apple does"? What kind of circular statement is that? It's true because it's true? When in the past has apple delayed a release of a product to coincide with an event? I could see if you were talking about one of the big annual apple shows, but that's not what this is.
To answer your question, no. I think they know approximately when the machine will be ready ahead of time, and schedule the event once they know that date. After all, much of the time they only announce the event about a week ahead of time, right? And in many cases, apple has an event to announce the new machine, and then the machines "magically" ship a few weeks later!