The article compares the 2.4
The article compares the 2.4 Turbo Outback with the 2.4 Turbo Wilderness. So the milage drop isn't from the new engine it's mainly from the change in the final drive ratio with the added weight, off road tires, and wind resistance contributing. If make those changes to the 2.5 or a 1.8 forester you may see an even larger drop in MPG since they will have to work a lot harder.