Checking the 2009 SAT data table, over 41,000 students achieved at least 750 on the Math section of the SAT in a test sitting and about 25,000 achieved at least a 750 on the Critical Reading section in a test sitting. Over 16,000 achieved combined scores of 1500 in those two sections in a test sitting.
SAT Data Tables
Most of the "top" Universities in US News, and all of the LACs, enroll relatively small classes. Without doing the math, my guess is that the 1/4 of those admitted freshmen that are represented in the 75th percentile you are referring to might fit rather comfortably in the numbers reported in the SAT test tables.