There is a factor that may be distorting the results a bit: are the IQs adjusted for age? Other than that, the data indeed suggests that metal-heads as a group may be the laggards. However, I would like to know what the margin of error is in the study before drawing any conclusions.
Also, the data seems to indicate a bias toward IQs for those who listen to music outside of the mainstream, though methinks the exceptions of reggae and gospel could be attributed to racial IQ differences, though compared to an average population with the same racial composition, I would wager it would be higher.
Digressing, is there an introductory thread?