If this is to be a *roleplaying* game, then there needs to be enough believability and consistency in the game world to allow me (as player) to play my role (as character), at least somewhat secure in the knowledge that something that worked in x-y-z manner once will do so again in the same situation. In other words, the "fluff" that is the world my character interacts with needs to be supported by the "crunch" of the rules that govern how the game works...the two should be seamless. How hard is that?
Example: FLUFF: As the ship sails off despite our party's best attempts to stop it, my fighter wearily drops his sword and it falls to the ground. Then, in a fit of frustration he rips off his helmet and vainly throws it at the fast-retreating vessel; it sails out over the harbour in a graceful arc before splashing into the water and slowly sinking.
CRUNCH: A sentence in the DMG "Assume gravity works much the same in the game world as it does on Earth."
Simple. Seamless. No headaches.
Whether that believability and consistency comes from the rules (where it should) or the DM (where it usually does) really doesn't matter very much, as long as it is present.
As for PCs and NPCs being different, I really disagree with the apparent 4e philosophy where PCs are heroes before they start. I'd far rather have every adventurer come from a non-adventurer's background - be it noble, common, or whatever - and by their deeds *become* heroes. The same rules apply. And yes, commoners should gain ExP if they survive a tornado...but they'd need to survive an awful lot of 'em to start gaining levels.
In other words, 4e will be like the mid-series movie that needs a prequel or two to explain how things got to the start point.
Playability vs. realism: if realism can be preserved without affecting playability too adversely, then preserve the realism. How hard is that? (and yes, everyone will have different ideas on where the boundary of "too adversely" lies; so be it...)
Lanefan