I feel like there is merit to the "Rulings are better" side of the argument. For instance:
1) It speeds the game along.
2) It helps the GM maintain Genre and Tone of their game.
3) It allows for player creativity to make a difference.
4) And, it relieves the burden of the GM to memorize and understand every single rule in the RPG text.
These are all good things and should be considered before opening the book and looking up a rule.
However, there is one key advantage you lose when you routinely adopt a "make a ruling" approach to most rules confusions:
1) It penalizes players who take the time to learn the rules.
So, I play with two groups regularly (about once a week each) and I attend two gaming cons a year. We usually let all the players know what the next game will be in case someone wants to learn the rules, get the book, think about what character to play, etc. To be honest, this does not happen among our players very often. In most cases players come to the table like a blank slate and the GM has to teach them the rules as they make their characters and play them. This is not so bad.
Once in a while, you get a player who likes the system well enough to invest the time to learn it. I want to encourage that behavior. I want to reward the player that has read the book by making sure their knowledge pays off. When they ask a rules question based on their understanding, and the GM makes a "ruling" that makes sense to them, then the GM is marginalizing (And possibly even penalizing) that player's inquiry into the rules for the system they are playing. To me, this is a bigger negative than taking 10 minutes to look up and discuss a rule. And to be frank, my RPG sessions are short, usually around 2 hours, so 10 minutes is a huge burden, time-wise. Still, it is nothing compared to thwarting a player's efforts to learn the rules in my opinion.
Of course, the true solution is that a skilled GM uses a combination of techniques. There are times when quickly making a "Ruling" is the best course and times where looking up the rules is vastly superior. The trick is to understand what you gain or lose when you choose a direction to go and make sure that is the affect you want that decision to have on your game.