I think you're right about the reasons for not upgrading. For orgs still using IE6 and XP, statistically it's very likely they're not going to be doing new development in PHP 5.5. (statistics pulled from thin air based on 15 years of experience with PHP and orbs who use it).
There's not been any security patches for PHP 4 for many years, but people still use it. Those same sorts of orgs will continue to use stuff out of date and unsupported for any number of reasons. Catering development processes around an increasingly small number of users doesn't make sense.
There's not been any security patches for PHP 4 for many years, but people still use it. Those same sorts of orgs will continue to use stuff out of date and unsupported for any number of reasons. Catering development processes around an increasingly small number of users doesn't make sense.