Engines design plays as much part in extending plug change intervals as does the design of the plug.
The platinum plugs that are stated to go intervals such as you speak are specifically designed to a particular engine and cost anywhere from 3 to 5 times as much as those gimmick platinums. You are real lucky to get that service from those plugs. Use the archives if you don't believe me. BTW I have never seen those plats last till the electrodes wore down as your picture shows. Bosch had some form of gauges to measure it but I had never seen a whole set make it far enough to see it; interesting!
Yes as to the oil consumption. since they have been there so long my guess may be off, but the plugs at the left end show oil carbon on the electrode and insulator.
Bosch Master, ASE Master, L1
33 years MB technician