Why does the modeler allow the Commit option on NPEs?
I noticed that for both Create and Change actions, if the object is an NPE, the modeler does not complain if you choose to Commit. Is there a technical advantage to this, or is throwing an error/warning about this just a low priority?
This is not correct. By Commiting a NPE you're storing the current state (though not in the database) such that you can rollback any changes to the NPE after this point.
When using NPE in your views and you don't commit them, a standard Cancel button may rollback your NPE causing it to be deleted.