I did learn that different.
I was taught to have just a bit of your own car in the side-mirror, to have a reference point when judging the position of cars around you in relation to your own car.
And a car that is behind you should be visible in more than one mirror. The center mirror has a pretty wide angle to give you a general overview of whats happening behind you. The side mirrors are for "detail view" to either side. That's what I was taught anyway.