Well, here is the thing.

EVen, Wizards of the Coast, in their books, state that for Versimilutude (sp?) and suspension of Disbelief, the campaign world/locale should mirror the real world with a few caveats.

It is after all a FANTASY world. so having a locale where the Trees Walk, or a mountain floats, or rivers flow uphill is a good if not required idea. Fantasy lore is filled with areas that defy the natural laws.

But to take this further, while this does not quite connect to the outside world, in WotC's Dungeonscape hardcover (a phenomenal book by the way and greatly recommened, along with their Cityscape book), the dungeon is probably the one local where there SHOULD be areas that defy physics. Rooms with no gravity, floting rocks, etc. These areas are actually expected by players and oddly, no one bats an eye when they enter a room where the very walls flow with blood!