Fixed and Flexible Rules

In most games, because of the competitive nature of the game, the rules need to be fixed, clear, and (hopefully) complete. At no point during play should you reach a point where you have to ask "what happens now?", because if you've reached that point then you are in a position that someone has to make a decision that will favour one side or the other. (Note that this even applies to games with an impartial referee in place - the job of the referee is to apply the rules, not to cover for any holes in them.)

Due to the cooperative nature of roleplaying games, however, an exception can be made. Provided the players trust the GM to be fair, the rules don't have to be fixed and complete. And this is a good thing, because the range of scenarios covered by roleplaying games is vastly different from other types of games.

This gives the designers of RPGs a choice: they can either attempt to provide a comprehensive ruleset, covering as many possibilities as possible, and trying to eliminate the corner cases; or they can leave sections of the ruleset vague and flexible, and let the GM fill in the blanks as needed.

(You can see examples of both approaches in D&D: 3e and 4e both attempted to provide comprehensive rules; 5e has deliberately been designed with flexibility and GM rulings in mind.)

I don't think there is a 'correct' approach here: many players will enjoy the security that comes from knowing exactly how things will work ahead of time... but any attempt to provide a complete ruleset is ultimately doomed to failure.

However, there is definitely at least one 'wrong' approach, which is to write an intentionally vague and flexible ruleset and then to start providing large numbers of "official rulings". Because what that means is there actually is a 'correct' way to play the game; it's just that the designers aren't going to tell us what it is.

If the game is intended to be left open for GM judgement calls, then leave it open for GM judgement calls. Don't immediately start closing up all those gaps you deliberately left in place!

(Of course, the above doesn't apply to places where the rules are simply mistaken - where they simply don't say what they were intended to say. However, even that isn't really a place for 'official rulings' - that's a matter for errata.)