The model works perfectly well with PHP -- put your data in a relational database, put your business logic in a middle layer of code, and implement only the minimally required processing at the page/presentation level. PHP supports that, while not requiring it.
While PHP can interface with servlets and COM objects, it's more common that the middle layer be written in PHP itself. (Significant extensions to PHP, such as graphic-manipulation, XML parsing, or database-access code, generally are written in C, compiled as libraries, and glued into PHP using interface code. See the PHP sources for examples.)
As PHP is a runtime-compiled language, there is a theoretical performance penalty, but you should run comparative performance tests before concluding that the theoretical and the real have much to do with one another. Java and application servers introduce their own layers of performance interference, you know.
Additionally, tools such as Zend Cache and APC compile PHP code into memory-resident images that can accelerate performance of frequently accessed routines.
One last point: Premature optimization is the root of all evil. The problem with most Web sites and most site production technologies is that they are badly designed and infested with bad ideas. It is extremely important that changes, improvements and reimplementations be facilitated. As a runtime-compiled language, PHP accelerates the change-and-test-and-change cycle that is crucial to the healthy development of any site.
