Just so everyone knows, that whole brothel thing is an urban legend. Lots of colleges think the law is there, but it isn't. St. Louis just got it's first sorority houses at University of Missouri, St. Louis (UMSL) and they looked into the matter.
Also check out Snopes.com
http://www.snopes.com/college/halls/brothel.asp
There are some zoning regulations that might prohibit sorority and fraternity houses. However, usually the school just prefers the lack of housing.
Bascially no one has ever found a law saying that more than X women living in a house equals a brothel.
*Kinda wishes SLU had houses, but I liked the all-Greek dorm and I like living with my friends, Sigma Kappas, other Greeks, or non-greeks