IQ scoring is routinely adjusted so that 100 represents the mean. It should be expected that IQ scores for college grads trend towards 100 as higher percentages of the population go to college. University is also not designed to maximize standardized test scores the same way that public high school is. I would expect recency and intensity of math education to play a higher role in IQ scores than the specialized knowledge and exposure to the arts that comes from a college education.