In MNG-6981 included aggregator projects (parent poms) the reactor will automatically include its child modules.
Falko Modler reported on the dev mailinglist that the exclude behavior (-pl !<proj>) does not do that at this moment, which it should.
The issue should be easily fixable by changing the DefaultGraphBuilder and its unit tests.
One point to note here is that I cannot think of a backwards compatible workaround for the old behavior (for
MNG-6981 it is done using -f and -N).