Dalrymple quotes John Gruber's musings on the idea:
I'm thinking it makes more sense for Apple to hold two events. First, an iPhone event, focused solely on the new iPhone and iOS 6. Then, the iPhone ships nine days later, and there's another wave of iPhone-focused attention as the reviews come out. Then, in the first or second week of October, Apple holds its traditional "music event", exactly along the lines of the events at which they've been debuting new iPods for the last decade.
He then captions the quote with, "Oh that Gruber is a smart fellow."
Dalrymple is considered an authoritative source on Apple news and is often used by the company to release information publicly.