you are right this case is only for the the exec-war and exec-war-only goals.
Here my situation, I want to package several wars in one exec-war, so I have created a pom project which depends on these 2 wars and use the tomcat7-maven-plugin. The version of my war are declared in the dependencyManagement of my parent pom. That give me the following structure :
-> project war 1
-> project war 2
-> packaging project and tomcat plugin
This way when I release the parent all the versions are correctly set (which is not the case if I use a property). The warRunDependcy needs a version number, so when i release my project the versiond of my wars are not change in the plugin configuration.
And it's the same when i use the extraDependency (which include some library to the tomcat like the database driver or some specific stuffs).