Spark Plug Question

That looks pretty darn good to me, and oil does collect like that on the threads.
My theory is that there is always a little oil in the cylinder left over after the rings scrape it down and this oil can't be burned off because it got caught in the threads.

Of course one would have to be sure it's not getting there from a valve cover leak or something, and soaking the threads when it's pulled out.
I don't see any oil above the sealing edge though.