Imagine the car market being that there really is only one car maker that counts, they make cars in two variant: a car and a truck, that's it. Now that they ahve all the market, they start to try to build parking lots and make it so that no that their cars can park in their parking lots but no other, and that other parking lots become incompatible with their cars. Well nobody would want it would they ? But they are sneaky: they bundle the parking spot in the price of your car. In order to buy market share they will undercut the price all other are able to offer by making it "free". Oh well those buying cars are sponsoring it, there's no such thing as a free lunch.
Letting them unbundle it means they go: oh but the price of the car stays the same minus the parking privileges. It's not going to make a difference if you let them do that. OTOH: is you want to bundle the parking with the cars fine: but the cars have to come with a choice in were the driver want to have his parking rights from all parking lots. Now this will again allow the real costs to come into play, force them to keep compatibility and allow competition to play.
Is a car company not having a monopoly ever going to be able to pull this off and gain a new monopoly in the parking business? Surely not as they'll be outpriced on their cars all too soon. But once you have a monopoly it's too easy to gain other monopolies at the expense of the consumers "forced" to buy from you. The consumers in the monopoly market and the vendors (and ultimate the consumers too) in the other markets have to be protected from the monopolists.
[edited by: swa66 at 5:54 pm (utc) on June 2, 2009]