Which is fine -- we do shoot for some kind of internal consistency and some kind of congruence to the reality we're trying to emulate (real world physics, TV physics, movie physics, fiction physics).
There are some things that we don't tackle because, really, part of the game is an escape from reality. You can talk about how (like other media) RPG holds up a mirror to our reality, helps us realize truths, and so on and so forth, but you can't get away from the fact that we're selective about what truths we try to tackle. For example:
- how often do your PCs have to answer the call of nature?
- how often do they suffer from colds or the flu?
- how often do they catch an unforeseen mundane disease and die from it?
- how often do PCs deal with things like cancer, heart problems, gout, and so on -- unless they get points from it in a point-buy system?