The punctuation/indentation already give you structure, all the highlighting does is break up the flow of actually reading. It essentially forces a micro-reset every second or third word rather than allowing you to seamlessly scan to find what you're looking for. It looks unreadable on the blog post because they have an unreadable font that is way too spacey (nothing against pixel fonts, just their particular choice of one...), but it really is way easier to read code if you try no highlighting with a real font.

I will caveat this on the fact that I use Allman brackets, and have even stronger opinions about that. K&R brackets are cancer and completely destroy the structure of code, so maybe that's why some people feel highlighting is necessary for "structure". With allman brackets, the punctuation guides your eyes to the indentation forming a clean box around each level of code, while if you draw a line from the opening bracket to the closing bracket with K&R style, half the code will be inside it and half outside it, bisecting the natural structure.