Umm, Cliffy recently tweeted that he's NOT making a horror game and that he's NOT in San Francisco (implying that he, and by extension Gears 3) wont be at X10. So the OP pretty much has it dead wrong lol.
Gears 3 was always going to be a tough release in 010, MS wont put their marketing muscle behind two of the same type of game at the same time, and of course they have Reach. Much as I'd LOVE Gears 3 ASAP, it's probably 2011.
Oh and that guy who was talking about Gears innovating...dont forget Horde mode..while it probably wasnt technically the first of it's type, it did popularize it, and we already saw ODST mimic it with firefight mode, and will see many other games do so in the future.