Of course, he’s talking about book sales specifically in the category of programming languages. As a Ruby advocate, the best part for me was the statistics for Ruby book sales compared to other dynamic languages:
Ruby continues its meteoric ascent. In book sales, it is now slightly larger than Python, 80% the size of Perl, and 1/3 the size of PHP. As more publishers jump on the Ruby and Rails bandwagons, we expect these numbers to grow even more significantly next quarter.