How is this different from dotnet20/mfc42/etc.?
MS Java used to be bundled with (some versions of) Windows? (If an application was released requireing XP SP1 before the release of SP1a, its developer might have assumed that Windows will include the Java VM) (With IE completely removable under Win 7, it might be even more similar...)
http://en.wikipedia.org/wiki/Microsoft_Java_Virtual_Machine#Windows_XP
This is different from what Scott reported. The MS Java VM only allows one to run Java applets within IE, not to run applications from the command line. The latter requires javaw to exist and be in the path, which Sun's JDK/JVM will do, but not MS's.
Frankly, applications that assume Java is installed are just broken. --Juan