Unfortunately several of the most popular PHP based platforms will be stuck using PHP 5.9 or older for some time. Magento just recently in version 1.9 added support for PHP 5.6. There are still an allarming number of Drupal 6 based sites out there in large scale production that have trouble supporting PHP > 5.4
The recent releases of Magento 2.0 and Drupal 8.0 should help move more sites to modern versions of PHP, but there is a lot of work still to be done on contrib modules to get full functionality out of M2 and D8