Well, let's think about this for a second. What are the stereotypes of sorority women? Partiers, yes, but what else? Rich, stuck-up, blond, gorgeous, and dumb all come to mind. The sisters of Sigma were none of these. They were intelligent, they were all shapes and sizes, they were not blond or snooty, and a few of them even wore glasses.
And they made it plain that they disapproved of the "Girls Gone Wild" reject behavior displayed by some of the pledges - something the stereotypical sorority girl would not do.
No one on that show - not even the "problem pledges" - fit the prevalent "sorority girl" stereotype at my school (that is, an overly perky blond girl with no brains and an entire wardrobe from Abercrombie & Fitch).
If you take this information and combine it with the fact that women like Jessica and DeDe were initiated, it's not hard to see where some people who hadn't thought about being in a sorority before might consider it after watching this show.
Or maybe I'm just looney.