Daaah. It doesn't appear that an EAR DD is generated by default for a new WAS v7.0 project.
Java EE -> Generate Deployment Descriptor Stub will generate the application.xml file. Afterwards, the EAR DD editor will launch.
Is there a change in the JEE 5.0 spec that makes the application.xml optional?
Sorry if I've wasted anyones time.
Thanks.