Sorry for being rough. It’s just that PHP should be shot in sight, when possible, to prevent further damage to the codesphere.
“Java, C++, PHP, whatever is not the issue.”
Kind of is, kind of isn’t. An open source project usually needs a pool of qualified developers on some common platform. It’s a balance between “enough good programmers can use this” and “it’s easy enough to get the job done with this”. On industry you hire under a profile; in open source you try to maximize the chances for a volunteer.
“The technology used is secondary.”
Up until the design phase, yes, mostly.
Java is not about the Java language itself, it's about the JVM. And the fact is, Java JVMs have been getting faster and faster. Also new languages, like Scala and Groovy can run on the JVM. I know people just love to bash Java, solely because it's the big dog. Syntactically, I prefer other languages, but the fact is, almost any problem that needs to be solved, has probably already been solved in the Java space, and has been used across many enterprises.