WVU actually had a decrease in alcohol related incidents.
My buddies and I have been around the bush on this topic, and we think the real reason ISU isn't doing this is the perception that it would effect tailgating. ISU tailgating is what keeps the football program well attended through bad years, and pretty much everyone knows it. If you let the stadium be the party, it cuts down on the desire to pregame, which reduces the scope of the pregame scene, and thus reduces the number of people coming into the game.
It's not a moral thing - we already sell booze to 20% of the people coming through the gate. It's not a risk thing either - many other schools in our position have done it without consequence. It's a very calculated move to not kill the golden goose.