Very interesting page. I would ask the following, however as you investigate this topic further... you'll soon become the PHP vs. Java guru.
Your comparisons are interesting and well thought out. I would also add some higher-level (less computer-science oriented, simply because the task at hand is generating web pages 'on the fly'). As a pure CS language, there is no doubt that Java is superior. But as a web page generator, I have moved from a Java-centric approach to a PHP approach, leveraging servlets or beans as needed "under the covers".
Therefore, some higher-level things to consider:
1) Compare the complexity of real-world production applications (postnuke.com vs ? in content management, phpbb.com vs. ? in discussion boards, jpgraph vs. ? in graphing). In my mind, the proof is in the pudding - which technology results in the better, more production-ready applications? They may be out there for Java - I would just like to know where they are and who is using them.
2) Compare slinging (generation) of markup which is where PHP excels (as it was designed to sling markup - this includes features such as character transformations, variable accessibility, web page captures (see the fopen call which captures a web page in a single function call). Your point about a string being encapsulated in a string class is somewhat irrelevant if you are a programmer cranking markup. Embedding object-oriented code into a page can be much more painful (and slower to execute) than leveraging traditional coding techniques.
3) Compare native database and directory support. Java would have the advantage in generic database access (JDBC) but PHP has the advantage in LDAP support (JNDI has several bugs which we have run into - quite painful) and native database access (e.g., Oracle or MySQL integration).
Overall, well done - and a very popular topic! It's worth building it out further.