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And Java clustering, for example Coherence, is a real turd. Expect Coherence to eat something over 50% of the performance of your app, which means that your app slows down when you add a second server, and doesn't get faster until you have three. ENTERPRISEY.
And yeah, you can code Java the same way as PHP, not using shared resources. The point being made is that you can always add more boxes for your PHP app, but such scaling breaks tons of Java enterprise apps (but not all) for the simple reason that the different threads communicate using shared memory.
Not trying to say PHP is good, just that it is easier to scale PHP than Java. Just like it's easier to add cargo capacity to a train than it is to add it to an airplane.