This is an interesting article I just read about Dave Arneson and DM impartiality.
http://beyondtheblackgate.blogspot.com/2011/07/dave-arneson-and-impartiality-in-temple.html
I'm not sure I want a DM (or to be a DM) that will grab a coke while you fight lizardmen (roll for both sides, please) but I do like his general approach. It's about the enjoyment of the game, the story and having fun, rather than about rules. Love it.