My understanding is that Eastern was the first airline to conduct powerbacks, and that it was a source of some labor controversy when it was first done (not sure why, as people have already indicated that it doesn't lessen the number of ramp employees required for the jet to push back).

As for breaking the flat spot on the tires, I think this is done going forward because the engines are more efficient in "normal flight" mode and thus better able to break the flat spots rolling forward rather than rolling back.