In reply to Mitchell.

WordPress itself will work on any php version greater than the minimum requirements.

It is indeed those older programs, some of which are no longer maintained, but still used, which holds back the defaults. The truth is that PHP is not very backwards compatible.

On the whole, getting the existing versions changed has to be an opt in process. But, getting the "defaults" changed for new users is totally feasible. The default should always be the latest version installed on the system, IMHO. And I think more hosts are starting to see that.