This way the demo pages are as succinct as possible, the code isn't confusingly intertwined with the html/css/js generated by their CMS (in this case WordPress)

This way the demo pages are as succinct as possible, the code isn't confusingly intertwined with the html/css/js generated by their CMS (in this case WordPress) and matches as closely as possible what was described in the corresponding article. It's also a fraction easier (saves finding a per-post css/js plugin), you don't have to worry about wierd interactions with the CMS code, and it will continue to work even if you change the CMS or theme.