The web hosting industry is rapidly changing. In the early days you had traditional hosting, but now the web is seeing a shift towards scalable PaaS and managed web hosting.
With traditional hosting, you were stuck with whatever version the server was running by your provider. If they were running PHP 4 and you wanted to build a PHP 5 app, you were just out of luck.
With cloud offerings you can generally choose different version of the software whether thats PHP or MySQL instead of just a single version fits all.