PHP is purely stateless. processing can not live beyond the life cycle of the request response loop. The article downplays this as though the only thing persistance is used for is storing cookies and session data, very backward thinking. This is trivial when building old school web applications but is a huge deal when running real applications which have a web interface. Try building an application in PHP which takes a data set, processes it for and hour and then stores the results for the user when they return. You could hack together a php / c application that'd probably involved a couple of shell scripts, a cron entry, and some major security holes. JAVA makes this relatively easy, secure and self contained.
Another issue totally ignored is that php is strictly a webpage tool. Try writting a client app that does it's core busness logic on a server, let's say via SOAP. That's not very scalable. Yes I'm familiar with the cli and that quirky tk interface.
php is not scalable precisely because it is not an end to end solution. it does simple web apps and does them very well. it shouldn't try to be Java, they are two totally seperate beasts.