While that is true, its doesn't always make for good storytelling. Lord of the Rings is an incredible piece of fantasy. How much would the plot have been derailed if Frodo and Sam took the One Ring and jumped into a pair of F-15 Eagles and flew all the way to Mordor? Or if an emotional scene in Game of Thrones was interrupted when the DeLorean from Back to the Future showed up because Biff typed in the wrong date into the time circuits? It is important when trying to tell a story to keep themes consistent. This is especially true in Fantasy, since a fantasy world has little or nothing in common with the real world. This applies not only to games, but to books, movies, television, even music. Any medium in which you are trying to convey a particular message or attitude to your audience. Introducing elements that are out of place will distract the audience and can easily "break the spell" of storytelling.