Sitting down to play Super Smash Bros. for the first time is an overwhelming proposition for the average adult. The game is a flurry of action, a camera moves in and out constantly, and the winner appears to be randomly chosen at first. To top it all off, all characters start out at 0% (you're not told of what), a percentage that is increased every time they are hit. Without instruction, most adults would give up on this game fairly quick, resigned to the fact that it's something they'll never get.
Kids don't do that, though. They just keep playing the game until it makes sense. This probably should be expected, since kids are usually in situations that don't make sense, so perplexing video games don't seem all that different than anything else. Adults, however, have cultivated a lifetime's worth tricks that help them spot the right patterns to quickly make accurate predictions. Once something requires that they detect new patterns, instead of building upon past patterns, adults usually opt out. One reason is that it quickly becomes difficult to think outside of established patterned thought, and another reason is that adults realize that figuring out every video game that comes along is not a high priority.
Developers seem to understand part of this--something along the lines of "you can't teach an old dog new tricks." Games that are built for adults recognize that the adult will have a difficult time learning a new gameplay mechanic, so they rarely add gameplay mechanics to established patterns of gameplay. This does solve the problem, but it's not the only solution, nor I think, the most ideal.
Adults are capable of learning new patterns, they just need more help in finding them. The fast pace of Super Smash Bros. is not conducive to this process. Adults see a blur of random events that seem to almost willfully contradict any potential pattern the adult may be trying to apply to the situation. As opposed to kids, adults live in a world that largely adheres to established patterns and is a comfortable place to live in--parts of it that don't conform to these patterns are largely ignored, mainly due to the discomfort they create.
This calls into question how difficulty in games has been thought of for the most part--specifically making it so it's easier for a novice player to win, "dumbing the game down," so to speak. However, making the enemies "easier" to beat will not make any difference to the player who doesn't understand why sometimes he wins and sometimes he loses--in fact, it could make the situation worse by affirming a pattern that should be ignored to actually understand the game. As we said in the post about grokking, winning is a sign of grokking, so if a beginning player is winning, that player believes he is making progress in understanding the game. In essence, by allowing players who don't understand the rules to win, you are helping them learn the wrong things, which will ultimately lead to frustration when the established patterns stop working as the difficulty increases.
What a new player really needs is not coddling, but clear feedback on the success of her actions. Arkham Asylum's fighting mechanic does a great job with difficulty. The most apparent goal--beating up the bad guys--is also the easiest. As players get used to the mechanics, they begin challenging themselves at more difficult tasks, such as beating up the bad guys without getting hit, or the final challenge, beating up the bad guys in one unbroken combo. This also happens to be the most highly rewarded goal in this area of the game. The levels of difficulty are organically built into the mechanics: by slowing down the entry-level gameplay, the game can layer more advanced gameplay into the temporal cracks.
So slow it down, don't dumb it down. Keep your great new gameplay mechanics, just make sure that people can see them at work.