Unless the top 10% has some systemic advantage at taking IQ tests. Type words into a search engine for further inquiries in this area.
Obviously, it's possible to imagine a world in which IQ is not largely heritable, and in which rich people pay lots of money to game their kids' IQ numbers, and then the kids somehow use these IQ test numbers to get better jobs (even though IQ testing from employers is basically illegal).
But we can adjust for that. I'd be happy to do the same bet controlling for parental socio-economic status.
You don't need to imagine that world, we live in it. Kids who go to private schools with SAT prep classes and practice the test dozens of times are at a several hundred point advantage to kids who don't. This gets them into better colleges which gets them better jobs and gets them better income.
As for what it actually measures (as opposed to what it trys to measure), opinions differ...
http://en.wikipedia.org/wiki/SAT#Correlations_with_IQ
"Frey and Detterman (2003) analyzed the correlation of SAT scores with intelligence test scores.[20] They found SAT scores to be highly correlated with general mental ability, or g (r=.82 in their sample). The correlation between SAT scores and scores on the Raven's Advanced Progressive Matrices was .483 (.72 corrected for restricted range). They concluded that the SAT is primarily a test of g. Beaujean and colleagues (2006) have reached similar conclusions.[21]"
"Certain high IQ societies, like Mensa, the Prometheus Society and the Triple Nine Society, use scores from certain years as one of their admission tests. For instance, the Triple Nine Society accepts scores of 1450 on tests taken before April 1995, and scores of at least 1520 on tests taken between April 1995 and February 2005."
At one point, the administration at CMU came to him and asked if he could figure out what was the best predictor of students finishing college. (Or it might have been just freshmen year. It's been a few years since that course.) He had access to all of CMU's data on students. The result: SAT scores.
Whether or not the SAT itself is a predictor of actual intelligence is besides the point.
On the other hand GPA's over 3 depend a lot on how hard your classes are, how heavy the work load, if you have a full/part time job which are less dependent on the student's innate qualities.
Of course SAT scores won't be predictive in that case. You'd want to look at SAT scores controlling for other admissions factors, which is basically SAT scores controlling for every variable admissions cares about, which of course means that no variable in particular has predictive power.
But if you want to see how strongly SAT scores correlate with academic performance, the way to do it would be to take some students who belong at, e.g., ASU, and somehow sneak them into Harvard.
The name originally stood for "Scholastic Aptitude Test".[35] But in 1990, because of uncertainty about the SAT's ability to function as an intelligence test, the name was changed to Scholastic Assessment Test. http://en.wikipedia.org/wiki/SAT#History