On the off chance that you're not kidding: That message is indeed intended for the operator of the site. PHP -- or rather, its creators -- probably assumed that they look at their own pages after updating their software, so they must have felt it's the most obvious and immediately visible place to display shtuff like this. (Often there's also text like "If you see this, please contact the site adminstrator"; maybe down in the fine print?)

As I understand it the problem is that nowadays, with sites / personal home pages being on hosted full-stack services in stead of each administered by its own proprietor on a co-located raw server, the hosting company updates stuff but may not even have any pages of its own to watch that use all the components it offers. And site owners (or "owners"?), on the other hand, may have uploaded their pages ages ago and not even looked at them in years, blithely unaware that stuff has been updated out from under their site.