I never bothered explaining this to the party. The one time I brought it up, I simply explained that this is a game...not a life simulation. We are willing to accept that elves throw fireballs at undead in a fantasy realm contained in a multiverse inhabited by gods and demons where reality itself is askew, but we cant accept that people can heal?
Dont stress it is my advice. Just play the game, play it well and forget the "realities" of the situation. My team leanred to let it go, and no kidding, we are having an absolute ball with our campaign.
Remember, stressing the small stuff does not make the game more fun, and that is what is important at the end of the day