I don't understand why any one would do put any restriction on linking to their site. I can understand banning linking to certain sites from their site, but th

I don't understand why any one would do put any restriction on linking to their site. I can understand banning linking to certain sites from their site, but the other direction? It's a bit like paying for billboards and painting them and then covering them up. Can anyone explain why any party would think it is a good idea to have policies that will reduce the possibility of news sites/random blogs/whatever linking to them and so reduce their page views? (And thinking that they can get people to pay for the "privilege" of directing possible customers their way?)