Because a *A award could include so many different flights and carriers, the revenue is probably shared based on a percentage of miles flown.

Using the example of a N.A. to Europe award in Business class using 80,000 miles transferred from Amex to Aeroplan, the discounted revenue would be about $.01/mile or $800.

A potential revenue-sharing scenario could work like this:

PHX - ORD (US) 1,439 miles / 12% / $96
ORD - ZRH (LX) 4,435 miles / 37% / $297
ZRH - FRA (LH) 177 miles / 1% / $8
FRA - YYZ (LH) 3,946 miles / 33% / $264
YYZ - PHX (AC) 1,874 miles / 15% / $120

While these revenue estimates seem ridiculously low compared to what Business class tickets cost on the open market, most frequent flyer awards are loss leaders (or followers...). Alliance members agree to make a small percentage of seats available in order to create a sense of perceived value for the frequent flyer members.

This scenario is complete conjecture on my part, so if someone has better information I would be very interested in hearing it.