UPDATE: Epic Games has just sent over this statement from executive producer Rod Fergusson on the delay:
"I know fans are going to be disappointed with the new release date, but rest assured that this is a business decision between partners, and not a quality issue. Gears 3 was on track to be the most polished Gears of War game ever when it released in April, and this additional time allows us to polish it that much more before it hits shelves next fall.
Next week we have a major multiplayer press visit at Epic HQ, and I'm really looking forward to the fans getting to see and hear about Gears 3 Versus multiplayer for the first time. Lots more exciting news to come."