Outbound flights leaving Canada/US may have little in fees, but what about return flights? You could easily get hit with surcharges of 1,000 CAD or more in addition to miles.

Try LHR to Canada on Aereoplan in business class - feel free to report out-of-pocket fees and surcharges.

Why different carriers charge different miles for redemption? Why certain airlines have fuel surcharges in their programs (e.g. Aeroplan) and others do not (e.g. Mileage Plus)? The answer is always the same, because they can. Being in one alliance has no bearings on how airlines create their programs.

Each program has its own sweet spot redemption, poor value redemption, and those in between. Your job is to find sweet spots, and minimize poor value ones; in other words, you don't have to stick with just one programs. I often fly separate tickets across alliances in both cash and award fares, and most on one trip.