Air Canada has been doing something like it for many years: Non-ref. coach earns only half of actual mileage or so, while full Y earns full mileage.
I believe that connecting flyers get mileage flown because the airlines want to compensate for &or encourage PXX to tolerate inconvenient connections. Why fly nonstop PIT-ORD when you can earn double miles xCVG or xDTW?

Remember NW's 500-mile connect bonus?
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Play the travel game 3 vacations into the future!