*snip*
This is all just a matter of semantics but I've always considered 10/10, 100%, 1/1 1093903/1093903, etc to be perfect, I guess thats just me. 100% means nothing is wrong at all and that is never the case (unless its a calculus test). You are right that scoring against different genres throws the whole thing out the window though. But that doesn't mean the scale shouldn't go up to 10, a game can get a 9.6 or whatever meaning it's damn near perfect but little issues take a down a notch. A professor of mine told me you should never get 100% on a paper because you can always do something better and I believe the same with anything that is subjective. But I suppose thats up to the creator of the scale to decide what a 10 means, awesome or perfection.
*feels like Bill Clinton debating the word 'is'*