DE Shaw is a pretty solid company. There may be plenty of people who are capable of trading without having come from top 10 schools, but they aren't really interested. They are looking primarily for highly intelligent individuals, and the SAT score is one indicator. I don't know anyone who can say they are truly smart but simply couldn't beat the SAT.
With that said, DE Shaw tends to be highly selective even at schools like Caltech, MIT, and Stanford requiring a 3.7 GPA to even get an interview.