Maybe it is not easy, but it is not impossible.
It's highly unlikely, as demonstrated by the PC port of Saints Row 2. If your PC's clock speed is higher or lower than 3.2GHz, the game will run faster than it's supposed to, because the in-game timing is based on the 360's clock speed. It's quite possible that there are many more games that would break down in the same way if they are run on the 1.6GHz processor of the Durango, which would not be acceptable for backwards compatibility.