Here you will find the explanation of the easyRentacar's way of doing business.
By offering one type of car at each of our locations, we avoid the expense of maintaining a range of cars that people only occasionally need
Also, they are taking advantage of the economies of scale. At the begining, they bought 5000 Mercedes Class A cars. I'm sure they got a higher discount than if they had bought 500 cars of 10 different models.
By operating from convenient locations with good transportation links, we avoid high-rent locations, such as on-airport sites, that would cause us to charge substantially higher prices
That's the same reason why
easyJet flies from small airports (such as Luton) instead of big ones. They got charged less for landing / taking off.
By setting a free mileage allowance, we ensure that those people who wish to travel higher distances meet the cost of doing so
This one has to do with the "dynamic" fare system that all companies of the easyGroup have (though I don't like it).
I understand the first two reasons. As for the rest of their conditions / policies, I don't know whether they are fair or not.
Regards,
Antonio