Calling All Spark Plug Experts, Opinions on these pics.

My records show that the truck has had 4 plug changes:

First change was Aug 2006 at 74k miles.
Second was Jun of 2010 at 110k miles, so
Third change was Jan 2013 at 140k miles. I had a pic but can't locate it at the moment.
Fourth was Jan 2016 at 170k miles

Here's a pic from plug change #2, June of 2010, 36k miles and almost 4 years on the set:



So if oil consumption is not up, what should I be looking for that could be causing the oil fouling?