People who play both are gifted and special souls who will be praised in song for years after the demise of both games.
I think you may be wrong, in that the folks who like both probably aren't particularly special. The people who like or play both may be far more common than we on message boards might imagine - they may well be the majority.
I would guess that most folks play one game or another out of mild preference, inertia, and/or convenience, not out of some issue written in stone that they'll never play the other game. Given the appropriate conditions (like, say, being invited to a game by friends) they probably don't care so much what game they're playing.
If we could recognize that strong preference to the point of exclusivity is not the norm, maybe we'd be better off in our discussions.