Yeah, the famous "yep" from Dalrymple is usually a good sign. However, the media would have you believe that Apple has confirmed it and that the leaked design is a for sure thing. The headlines all say things like "Sept. 12th release date confirmed for iPhone 5" and "iPhone new design confirmed". Don't believe those things for a second. Apple hasn't said a word, and they won't say a word.Yes, Jim Dalrymple confirmed the Sept 12 / 21 dates. He has sources inside Apple and has never been wrong. If he says "yep," believe it.
With that said, there is always a small chance that a problem in production or something else will force Apple to move the dates back. But at the moment, that's Apple's plan.