Books as a success indicator

Some people think they can measure somehow the success of languages with book sales (or here): "C# is gaining on Java, python is gaining on perl [...]" (2005). But perhaps it's just measuring the focus of a publisher and they don't print books people want. When looking at the JavaOne bestsellers, it's clear that others do print interesting Java books people buy. From the top ten listing there is only one O'Reilly book (3 from Addison Wesley, 4 from Prentice Hall and 2 from Manning).

"In terms of computer languages, PHP (up 16%) continues its strong growth. C# (up 2.5% over last year) was the only other programming language whose growth was in positive territory. By contrast, sales of books on Java (down 10%), Visual Basic (down 23%), C/C++ (down 4%), Perl (down 14%), Python (down 9%), and Javascript (down 12%) were all lower than they were in the same period a year ago." (Q1/2007)

So what O'Reilly really says is that they have interesting books for PHP and C#, but less interesting books for Java, Javascript and Python.