Java is plenty widespread. It's a good bet that most systems are going to end up with a JVM on disk somewhere after 6 mo - 1 yr of usage.
(And: The same people who install Eclipse, Minecraft, LibreOffice, or Photoshop are also more likely to have one of the apps that Flashback avoids co-habitating with: Little Snitch, Xcode, etc.)
It's simple to buy and install and get working. There is no reason to assume that Mac users running Minecraft are going to also have Xcode or Little Snitch.