Interesting data. My first reaction was that lisp and scheme are still underutilized and underappreciated.

But then, the metrics he's using wouldn't count downloads of the PLT books, or Shriram Krishnamurthi's Programming Languages: Application and Interpretation, and it's not clear SICP or EOPL would be counted as Scheme books in their reckoning. And that's assuming you accept popularity as a useful metric.