Leasing a vehicle, at least from the dealer's point of view, is determining the "residual" value at the end of the lease... that is, how much is the car going to be worth then? One of the primary indicators of that value is the mileage on the car. So... they base the lease payment, in large part, on the expected mileage. You can exceed the agreed to mileage but at a very stiff penalty. In our case, it's 15 to 22 cents a mile (or $150 to $220 per 1,000) for anything over the contract amount.
I would say that, there was a time that owning the car was a better thing since you had something of value at the end of the monthly payments. Problem is, that was when one paid for the car in say, 36 months... now, that same car will probably (at least here) take 60 or 72 months to pay off. By that time the car has depreciated so badly that continuing to own it has lost its value (no pun intended). Whereas, just walking away from the leased car at the end and re-leasing a brand new car makes more and more sense... at least to me.