OK, taking a purely logic (i.e. engineering) stab at this:

Why does the 2014 Forester rate +2 mpg with basically the same setup:  2.5L Boxer, CVT, AWD???

Logic would say the Forester would get worse, since it's more aerodynamic inefficient (taller, less sleek).

The Imprezza/Crosstrek do better due to smaller engine (2.0L Boxer) so that I can understand (as well as being smaller vehicles).

But I don't get why the Forester/Outback are so different in Highway MPG here. 

Anybody know the answer to this?

TIA

Only volkswagon people worry about mpg

Firstly, While they both have 2.5L boxer engines, they are actually different in certain ways. The forester engine outputs 170hp while the outback is rated at 173. I'm not sure exactly what causes this difference, but while this may seem minor, I'm sure that there is a well planned out reason, and that it does affect "things".

 

Realistically fuel economy always comes down to how hard the vehicle has to work to get moving, and then keep itself moving. The 2014 forester has a different (while very similar) Lineartronic CVT automatic transmission, so my best guess at this would simply be that the system in the 2014 forester is just more efficient in that regard. Being that the CVT in the Outback was last updated (as far as I know) in 2012 (at least for Canadian vehicles) where-as the forester's current CVT is New for 2014, I would say that this stands to reason. Or at least I would hope that Subaru is always trying to improve it's overall efficiency.

How do the weights of the two compare?

Does the Outback get the new FB25 engine yet? I'm pretty sure the Forester got that already. it has a couple more lbs of torque and slightly better mpg than the old EJ25.