Actually, there is a quite a bit of jobs that require PHP considering the plethora of sites built on Drupal and WordPress. I guess it depends where you live.
I actually intepreted that as the jobs require a very low level of skill and provide low compensation—exactly what you’d expect from making a job “blue collar”.
Most of the skill in that area is not working with the CMS but doing the crazy complex integrations that clients ask of them. (And of saving the work of not-as-skilled/too-skilled-for-their-own-good crowd.)