Engle Matrix Games used in RPG Character Development

What is the advantage of assigning a difficulty and then rolling dice, over, say, a "universalis" type of "story point" system? Isn't it frustrating if everyone wants something to happen, but the dice say otherwise? Isn't it kind of 'double handling' the decision - having two factors that decide if it happens? Also, when do people choose nubers other than 1 (if they don't like an idea) and 6 (if they do)? What's the motivation for leaving it up to chance?

Consider this alternative system:

After every game, every player (including the GM) gets three "story tokens." They can use these before and after games (and store them between games) to make statements about the game world, or their own characters. They do this by making the statement, and sliding the tokens back into the pot. Anyone can support the idea by spending their own tokes on it. Anyone can veto the idea by spending a like about of tokens. Points spent of vetoed ideas are still lost.

I'm not saying this is better, but what are the differences? Why use dice?