If this would be true, then "XML" and ASP would be the hardest languages. Also this would suggest that TeX for example is simpler to use than Python or Ruby.
Hence, "approximation". In particular, XML isn't a programming language, so questions about it are more likely to pertain to writing parsers and the like. TeX users may well have other sources for answering their questions. The approximation is very rough, but there is clearly a signal in the noise.