If they're using Java they could just as well use a Java video player. My guess is that it's closer to "off-the-shelf" for Flash, and the networking stuff is closer to existing code in Java. I'm sure those parts'll all be redone in Flash next.
Hmm, apparently a missing listen() means they have to bring in an entire second language and VM. I don't get why normal sockets are so anathema to web purveyors.