Well, 'judging events' is not the same as playing a role. And I'm not 'impartial'; I'm extremely biased. As the DM/authority at the gaming table I'm actively working to make sure everyone has Fun. I am utterly opposed to 'impartiality' if and when it causes a game to become Not-Fun. This is why I do not obey dice, for example. If you disagree, and think that bad die rolls that ruin a game session are unavoidable due to some sort of 'rule' or mandate for impartiality... then we'll have to simply disagree in the strongest possible terms.
Tom Moldvay (From the 1981 Basic D&D's DM Instructions section):
The players will often surprise the DM by doing the unexpected. Don't panic. When this happens, the DM should just make sure that everything is done in the order given by the outline or sequence of events being used. Minor details may be made up as needed to keep the game moving. All DMs learn how to handle both new ideas and unusual actions quickly and with imagination.The DM should make the adventure seem as "real" to the players as possible. All should avoid getting stuck in long discussions about rules or procedures. The game should move along with humor, as well as excitement.
Monte Cook (From 3e Dungeon Master's Guide and reprinted in 3.5's DMG)
While all the players are responsible for contributing to the game, the onus must ultimately fall upon the DM to keep the game moving, maintain player interest, and keep things fun. Remember that keeping things moving is always more important than searching through rulebooks to find the exact details on some point or spending time in long debates over rules decisions.
And of course, everyone's favorite(yes, it's ACTUALLY in all caps):
Gary Gygax (From the 1978 AD&D Dungeon Master's Guide's Afterword)
IT IS THE SPIRIT OF THE GAME, NOT THE LETTER OF THE RULES, WHICH IS IMPORTANT. NEVER HOLD TO THE LETTER WRITTEN, NOR ALLOW SOME BARRACKS ROOM LAWYER TO FORCE QUOTATIONS FROM THE RULE BOOK UPON YOU, IF IT GOES AGAINST THE OBVIOUS INTENT OF THE GAME. AS YOU HEW THE LINE WITH RESPECT TO CONFORMITY TO MAJOR SYSTEMS AND UNIFORMITY OF PLAY IN GENERAL, ALSO BE CERTAIN THE GAME IS MASTERED BY YOU AND NOT BY YOUR PLAYERS. WITHIN THE BROAD PARAMETERS GIVEN IN THE ADVANCED DUNGEONS & DRAGONS VOLUMES, YOU ARE CREATOR AND FINAL ARBITER. BY ORDERING THINGS AS THEY SHOULD BE, THE GAME AS A WHOLE FIRST, YOUR CAMPAIGN NEXT, AND YOUR PARTICIPANTS THEREAFTER, YOU WILL BE PLAYING ADVANCED DUNGEONS & DRAGONS AS IT WAS MEANT TO BE. MAY YOU FIND AS MUCH PLEASURE IN SO DOING AS THE REST OF US DO!
Sadly, while I enjoy 4th edition at times, it's written in "legalese" so the book says that you can run a game where you gloss over the rules and only care about immersion, but if your group prefers to instead debate rules for an hour, that's okay too. The whole book is unfortunately written in that sort of double-speak!
Maybe I've just failed to attend a game session where players ENJOYED long, drawn-out rules discussions, but in my experience, players and DMs don't tend to consider those sessions very fruitful.