Apparently, there's the open-source, Free Software OpenJDK, which is freely distributable and which Canonical still distributes, but there's also the official J

Apparently, there's the open-source, Free Software OpenJDK, which is freely distributable and which Canonical still distributes, but there's also the official Java binaries released by Sun/Oracle which are under a more restrictive licence. The official binaries for Java 6 are close enough to the OpenJDK implementation that most things run, and the official binaries for Java 7 are actually based on OpenJDK 7, but there's still differences. I've heard of Java-based production systems that were broken by a minor point-release of the official Java binaries, so it's not surprising to me that people would be skittish about switching to an entire other implementation.