Two parts: OpenStreetMap, the website, aims mainly to be a database and a great editing interface. So the end result is mostly the data, which you can download in full ( http://planet.openstreetmap.org/ ). They have a few sponsors to handle the bandwidth required ( http://wiki.openstreetmap.org/wiki/Partners ), and a few meaty servers ( http://munin.openstreetmap.org/ ). There could always be more, and the base of partners could easily increase.
Part two is that _tiles_ and design are a different matter - OSM.org itself has low limits on the number of tiles you can use from their server before they start pushing you to use your own server or another service. MapBox is one of those services, and basically we handle a massive amount of work & bandwidth, and price out the service based on how much these things cost.
Two parts: OpenStreetMap, the website, aims mainly to be a database and a great editing interface. So the end result is mostly the data, which you can download in full ( http://planet.openstreetmap.org/ ). They have a few sponsors to handle the bandwidth required ( http://wiki.openstreetmap.org/wiki/Partners ), and a few meaty servers ( http://munin.openstreetmap.org/ ). There could always be more, and the base of partners could easily increase.
Part two is that _tiles_ and design are a different matter - OSM.org itself has low limits on the number of tiles you can use from their server before they start pushing you to use your own server or another service. MapBox is one of those services, and basically we handle a massive amount of work & bandwidth, and price out the service based on how much these things cost.