Over Pronation, Under Pronation and Neutral foot fall.
I fall into the Neutral category, with the soles of my shoes showing an even wear across the entire sole, and little or no wear to the heel.
Its the way a person was born, and is very difficult to change.
People with severe motion control issues wear expensive orthotics, but i can remember someone i knew in Cardiff years ago, who even destroyed their orthotic insoles.
By the looks of it, you have a very mild pronation issue, as the wear to the heel of your boot is very mild.
Next time you walk down a highstreet, just look at peoples feet, and observe the way their feet hit the ground.