I can see that upwind engine failures may be "easier" to fly because the swing is in the same direction as the weathercock. However I can't see that the validity in the book's explanation that a moment caused by the crosswind opposes the asymmetic yaw of an upwind failure. My aircraft type has an engine-out ferry crosswind limit of 15 knots from the deadside - which supports the argument that there is less rudder authority available with an upwind failure.