Fair bit of negative camber on the rear, which, coupled with "gentle" cornering, could account for it. At 46K miles, even on the rear, I don't think I'd be complaining!
What pressure are you running them at and how often do you check it?
If you regularly check pressures something must be off at the back. My rears are wearing evenly across the full width. Unless you have the R then the rears are just pulled around so wear should be minimum.