Most schools design the rules based on how much space that they have available, and how much demand there is. More urban schools generally are going to have wider choices because they have to compete with the off-campus housing market, while more rural schools usually don't.
Some other factors that play in are the religious affiliation of the school (generally, religious schools are going to segregate genders more carefully), and the kind of money that is floating around, both in terms of the funding that the school has, and the usual socioeconomic-status of the average student. Schools that have affluent student bodies pretty much have to provide some options for high-end living spaces, or they will lose those students (and students who have family money are VERY valuable, because they grow up to be alumni who have family money and are able to make contributions that endow buildings and faculty positions.)
A good friend of mine has worked for 20 years now for the leading US builder/operator of commercially-run campus housing for public universities. They are all over the US. The deal for the school is decent; the company builds the building and usually sets up the purchase model that has the university buying the building from them over a period of about 25 years. All facets of building mgmt and room assignments, and rent collection, are done by the company. Housing almost always loses money and/or barely breaks even when a university runs it, but this company has perfected the business model for dealing with this community -- they even create separate leases for roommates living in apartment-type units, so no one gets stiffed if a roommate quits school. Their units have high occupany rates and they very seldom lose money, so I think that they are doing something right. In order to make these ventures profitable, the company is very careful to make these units appeal to the more affluent students at each school, at a price point that will make them popular enough to stay rented. Sometimes the properties are built on university land and sometimes off-campus nearby, in which case it is clear that you are renting the space from a private company and not the university itself.