[Cadaverous Pallor]

It's an interesting question - how much reality do you want in your storytelling? Should the president's name be correct or fictional? Which movie stars "exist" and which don't due to acting in the film itself? I love when movies play with that and have the actor exist anyway, so you have an actor saying that he hates himself or whatever. I can't think of an example off the top of my head.

More on realism:
On Family Guy, Stewie travels to the future.
Stewie: "Everything looks the same!"
Future Stewie: "What did you expect, it's only been thirty years."