It's obvious why there are two models. People who want the best quality will buy the Premium (which is a much higher margin item for Arc) and those who are price sensitive will buy the regular item. Economist's call it "price descrimination". The next time you are on an airplane (unless it's Southwest) ask your fellow travellers what they are paying. The last minute business person will be paying more than the student planning his long anticipated trip home.
This will start to break down for Arc when competitors introduce more attractive products priced lower. Peak and Arc matched pricing on their AAA lights when the products were introduced last year, but neither company put much effort in innovating those lights since then. (Other than Peak shipping its newer lights with a clip - big deal.) The new Fenix AAA lights will give both companies a real run for the money. Fenix still trails in build quality, but it makes up for it in better regulation and much better value. Look at the E0 and E1.
We don't see the numbers, but it's pretty obvious that Fenix is taking the industry by storm - and taking sales away from companies like Arc and Peak. Since they can't compete on price (vs. cheap Chinese manufacturing) Arc better keep innovating. Perhaps the new luxeon light will be the answer.