Heheheehhe, funny thing about fiction rules is that there's always some clever bastard that can violate them excellently.

Take M. John Harrison's Light for instance: a major plot point of the book was that all forms of FTL are true -- even the ones that contradict each other.

Having said, those rules still exist for a reason and you are completely correct. Internal consistency is key to any good unicorn-in-the-garden but especially in science fiction.