Unfortunately that is just wear and tear - you're lightly abrading the material every time you slide in and out (or over and across, as the case may be) the side bolsters of the seats. Seats with a totally flat back don't have this issue since you don't rub over them every time you get in and out.

I'm with Goldwing on this - yeah, it sounds a bit weird to say I'm picky about how I get in and out of the car, but it makes all the difference in the world. My car has 13,000 miles on it, mostly short trips really (meaning a lot of ingress and egress) and the seats look brand new.