My original prediction was the 22nd, and the only other original rumor is the 15th.. that's why I'm thinking we might hear something a week or two before either the 15th or 22nd.
Let's hypothetically say Mavericks is coming out on the 24th, and we get the rMBP unveil on the 15th.
What would Apple do in that scenario? Have they, in the past, released new Macs a week before the OS update came out?