The pie chart indicates that only 15% of companies use CSS? That's clearly the wrong way to display this data. Very few of the technologies covered are mutually exclusive.
I personally don't read many PHP related articles because, well, there isn't much new to learn. It's an old/stable language with well understood constructs.
Part of the problem is that the Rails community being as vocal as they are make it seem like everyone is using rails. In this case perception is not reality.
I'm not into web development stuff, but I thought currently big projects prefer not to use PHP. People say PHP helps them to find cheap programmers, but I dont think good PHP guys can be hired at low rate anyway.
1. In some cases the technology choices aren't mutually exclusive, as you point out. A better representation would be a bar chart that tops out at 100%
2. Not all technologies are equally detectable. The ones that are harder get penalized, and those that or impossible to detect are penalized 100%. In categories where this is endemic, the ones that are detectable appear to be dominant when that is hardly certain. Frameworks is probably one of the most egregiously misleading of the bunch.