LegacyMom,
USC’s average SAT (math+CR) is almost 100 points less than WashU/Northwestern’s. That alone indicates the latter are harder to get in. Many people got into NU without any visit while many others who visited got rejected. There’s no evidence to support your claim that they “care very much about level of interest”. It’d be very difficult to maintain their high stats if they limit their choices that way. Your clam is simply not fair to the kids that got in based on their merits.