Another theory there: when you look at pages with a .PHP extension, you are selecting for sites where they don’t know or can’t be bothered to use mod_rewrite or nginx config.
That tells you something about the type of site. In general, I would say it means the site is likely either old or not built by professionals, probably both since most non-professionals will be using WP.
It also means that no PHP site built with WP, Drupal, etc gets included in the analysis and that covers some very big sites like Weather.com and some big media sites.
semi-related story: back when coopster, jatar_k and I were PHP mods on wmw, Adam (I think) had a boss who went to some conference where someone (no doubt a Sun rep) said that the best tech that all websites should use was Java Server Pages, which was the wave of the future. So the boss comes back and says that to future proof the site and be on the bleeding edge of web tech, the whole site needed to be converted to JSP.
After some gnashing of teeth and rending of garments on the team about the colossal amount of work for no useful purpose, Adam went in, made a few changes to the rewrite config and few changes to how links were rendered and made every page on the site a .jsp page. They told the boss that the team had worked through the weekend and the site was ready to go. The boss was pleased to know they were now on the latest tech and fully future-proofed.
