Another survey available here allows us to look at income from work in 2002 by undergraduate major for graduates in 1993. Here are the 25th and 50th percentiles, respectively:
Note that income from work is a product of two variables. First, how much did you work? Second, what was your rate of pay? My guess is that a lot of people who go into education decide not to work after several years. That would really skew the mean, and perhaps the 25th percentile, but I would think that the 50th percentile would not be affected so much. However, even at the 90th percentile (not shown), education majors earn $56,000, which is way less than other majors. In other words, the 25th percentile among engineering majors earns nearly as much as the 90th percentile among education majors. Psychology is the next lowest at the 90th percentile, with $70,000.
At the 90th percentile, business and social sciences edge out engineering, although all three are essentially $100,000 at the 90th percentile. Overall, the 90th percentile is at $92500.
Social sciences and business have the highest interquartile range, meaning that they have relatively high within-major variation in salary outcomes. Engineering and education seem on the low end of within-major variation. I think that it's a coincidence that social sciences comes very close to the overall in terms of 25th percentile and 50th percentile. That is not the case for other percentiles, where it tends to be above the overall figures.
My view of all this is that it confirms my point that "college graduate" is not a homogeneous category. The economic effect of increasing the number of college graduates is going to vary, depending on whether you graduate more engineers or more humanities majors.