If a school is tougher to get in to, then naturally they are typically going to have a higher % of the top students. It makes sense that most students who get in to a CalTech can handle the work (and even then most of them consider their workload tough), while some people who got in to GaTech, especially in-state, wouldn't really know how tough it is until they got there because they figured they could handle it if they got in.
For instance, take Cornell. Many prestige whores choose it simply because its "IVY LEAGUE!!1" and a bit easier to get in to than the others. These people usually don't last long once they realize that Cornell is actually hard, especially if they do engineering. However, people who chose the school for its own merits, other than simply being IVY (it's "Ivy", by the way - it doesn't stand for anything), typically do fine.