I don't own 8 Ortlieb panniers because of their willingness to sell single bags. I own them because they are the best panniers I've ever used. That's far more important to me than what will happen in the unlikely event one is lost or stolen.
Say you're on the road, and a raccoon eats a big hole in one of your panniers... you stop at a bike shop and yes they have Ortlieb panniers but no you have to buy two... seems silly to me