If it says Ships by: Aug. 28 (normal preorders say Delivers on Aug. 28), and in the past, the UTD discs did not arrive on release date ... what logic tells you it will arrive on the 28th?
The logic that my pre-ordered iPhone 3GS also said "Ships by" when in fact the date was the delivery date. Also "Ships by" doesn't preclude it from shipping before the 28th, just by it., so quite possible for UTDs to arrive on Friday. At any rate it's all fun and speculation.