This stat shows that PHP is used by 75.2% of all the websites whose server-side programming language we know. http://w3techs.com/technologies/overview/programming_language/all
And this page shows that PHP is the least used server-side language in ranked by usage on top websites
http://w3techs.com/technologies/topsite/programming_language
Does this mean PHP is used for quick and easy website where other languages are used in more complex websites?
The language doesn't matter, it's the way you write your application. PHP has got a bad reputation over the years, which is (from my point of view) mainly caused by the bad quality of many scripts, boosted by the simpleness to write your application. (mod_php, wide availability in webhosting packages) Big sites like Flickr and Facebook are also using PHP (with other languages). To write a complex site you don't need to go with one technology, often it's better to use other ones ,for some parts, and let them work together to create something awesome ;)
