I think I can answer that question on behalf of myself and the others who are changing oil between dealer visits.
13,000 miles is a LONG TIME between oil changes, Mobil 1 or no Mobil 1. Call me annally retentive if you like, but frequent oil changes have never proven to have an ill effect as far as I can see.
Keep in mind that MB was advocating these long FSS intervals with Dino oil and are now paying the price. They are in a competitive situation and must tout less frequent maintenance requirements in order to be competitive in that category. That doesn't mean they are always correct, or that it is the best thing to do for maximum engine life.