I asked my professors (one graduated from USC, one from Penn, and one from Standford) this question and a few others, and they pretty much said the same thing.
1) the LSAT does not correlate with the school grades as much, but more with the bar exam success.
2) the smartest people in law school (if you are saying that the smartest people are the high LSAT people) are not the ones that get the best grades. The ones that get the best grades are the ones that can organize and get their thoughts on paper the fastest. Of course, if you got a high LSAT score and you can do these also, you will be in the top 25%.
In my first torts quarter exam, many people that got full rides (very high LSATs) ended up in the bottom 15% of our class. It seemed like most people that scored top 15%, above 85% or higher, had middle of the road LSATs.
Me personally, I got above the 75% LSAT score (but not that high, since I didn't get a full ride), but still got middle of the road, 79% on my first exam.