Great column this week, Yahtzee, but I would digress on a few points.
1. Mary Sue's can and do work in films and books. Perhaps the most iconic example would be Indiana Jones. He's handsome, smart, tough, punches people, gets to shoot foreigners with no repercussions, fights Nazis, says great sarcastic quips, has all kinds of women crawling over each-other to touch his long firm whip, and has a bad ass jacket and hat. His only flaw is a fear of snakes played for comic effect in each movie with no real consequence to be had from said fear. The Action Adventure genre is filled with them because the genre's main appeal is escapism via vicarious fantasy. To borrow from Plinkett, the appeal of these characters isn't the characters its being them. They're vessels for us to imagine our selves doing awesome things, having awesome adventures, saying awesome things, having everyone see how awesome we are, and hooking up with awesome people.
2. Mary Sue's fail when the world around them seems only to exist to emphasize how awesome the Mary Sue is, because everyone else in it is grossly incompetent. Take for example the Say No To Video Game Drugs episode (The Game) in Star Trek TNG, where Wesley Crusher essentially by himself had to save the Enterprise. Riker comes back from Risa a changed man, playing a virtual reality pong game 24/7, telling everyone how great it is. It was all he was talking about non stop like some kind of obsessed psychopath. Normally when people don't seem themselves they get sent to sick bay to start reasoning out what's going on, but whatev's let's all break character and put on this silly head gear cause Riker, with a thousand yard stare, told us its the shit. Thus Wesley is the sole voice of reason and wisdom in a universe where every adult is having too much fun tossing a disc into the mouth of a worm using their mind. We as an audience reject this kind of Mary Sue, because the world itself broke our suspension of disbelief. It is when the world devolves into some kind of solipsistic fantasy that cowtow's to one character that it begins to lose the audience.