The definition of preferable form if not defined in the license it is defined by the creator of the licenses intent, verified through statements or writings. If that is not conclusive the court will create it's own definition.
As the creator of the GPL defined preferable form numerous times in public writings and speeches that last step will never be necessary and the GPL's author's intent is not in question. RMS has stated several dozen times that the clause you are citing was to prevent the paper source code exploit. Since Redhat is not distributing source code by printing it out, the issue is null.