The equinox launcher starts the Java VM using the JNI invocation API. Because we are such good friends with SWT (and also because it is easier) the VM was always started on the first thread. This turns out not to be so good when you want to run Swing on the Mac. There was a conversation about it over on EclipseZone.
So I fixed the bug (181698) today by adding a new option to the launcher "--launcher.secondThread". Use it if you want swing to work. This option can be compared to the -XstartOnFirstThread for the java launcher.