Rules or Rulings

What if it's not in the game?
In his Afterword to the Original Role-Playing Game, Gary Gygax wrote:

There are unquestionably areas which have been glossed over. While we deeply regret the necessity, space requires that we put in the essentials only, and the trimming will often have to be added by the referee and his players. We have attempted to furnish an ample framework, and building should be both easy and fun.

Note that he indicates, "...building should be both easy and fun." A key component of the old school approach as I interpret it is adding to or altering the rules and setting of the game. This is under the control of the referee, who is encouraged to work with players to develop new content for the game that will reflect player interest, but no unbalance the game. Balance is primarily focused on having long-term fun and maintaining a believable milieu, one that is flavored with lots of warriors and priests and not overpowered by magic users.
Keeping it believable requires attention to the passage of time so that torches burn out and rations are consumed, so that injuries require downtime to heal if they are not cured by magic, and that starting characters are much like real people except a bit more heroic. It is only through a voluntary suspension of disbelief that players can become immersed in the shared fiction and make the game come alive in their imaginations. Otherwise it is just another game.
A large part of the appeal of the original three little brown books that come in the white box is that as referee I am encouraged to create. First a setting, dungeon, and/or wilderness, then adding procedures for play, the need for which may become evident during play of the game. The "framework" provided by the written rules is just that and some see this as a criticism of the original edition, but I see it as an opportunity for expressing my creativity and making the game just as I would like it to be. I freely admit that it is fun for me to make things up as I go.
How we answer the question, "What if it's not in the game?" can be used to define two very different approaches to role-playing. To say that "if it isn't covered by the rules, it isn't part of this game" is one interpretation. Players who adhere to this motto often prefer a rule system that strives to cover as many possible situations as possible. Players are encouraged to look to the rules for guidance on what is possible and how to resolve the outcome.
Another approach altogether is to say "tell me what you would like your character to do and I will suggest how we can resolve the outcome" is a much more open and imaginative approach to game play. It requires a degree of trust in the referee, who by definition is an impartial arbiter with regard to the game rules. Fun and balance should be foremost in the referee's mind when rulings are made. Consistency in applying rules should be striven for, but not at the expense of flexibility, which is one of the strengths of such a system.
It really boils down to personal preference. Some game designers, players and referees prefer having written rules that govern lots of things that may happen in a game setting. Others are happier with a framework of rules and the freedom to make ad lib rulings.