This is like when your carrier pays for the phone, lets say you pay 10 EUR per month for a mid class phone and 20 EUR per month for a premium phone. Looks like a small difference (+ a "price" for the phone)

If you buy both without a carrier, you might pay 400 EUR for the mid class phone and 800 EUR for the premium phone. The price difference no looks huge.

(The difference in acucmulated prices is the "buying" price of the phone)