There was a massive push from the community for PHP5. They had a similar site to the Python3 WOS and large projects such as Wordpress and Drupal announced PHP5 only major updates. I would link it, but the domain has apparently been left expire and replaced with e-cig spam. So here's some link to comments about the announcement: http://www.garfieldtech.com/blog/go-php-5-go , and then a post about its impact and a desire to to the same again for PHP 5.5: https://groups.google.com/forum/#!topic/php-fig/ogp03OHbVJ0

There were a few reasons why they pushed harder with PHP5 however, especially given the tendency of budget web hosts to use old versions of PHP4 with insecure by default configurations (register_globals etc.).