I support the TR4Q campaign...And when I do, nothing's more satisfying than showing them why tiers don't win matches.
See, the thing I'm trying to say here is that they do exist and they do win matches (not all by themselves, someone new to the game won't be winning matches left and right against everyone just because he's using Wolf or Marth and his opponents are only using Mario and Yoshi, there's more subtlety to it).
The way tiers work is that they're a general observation of the efforts you've got to put in in order to win, combined with all the options open at a character's disposal (combos, defensive options, maneuverability, killing power and a bunch of other shit). It's not really a "you shouldn't play with X" list and more of a "X has an advantage over the rest of the cast because he can do Y to Z while others can't". It's a simple concept really and tho it shouldn't really dictate who you pick (personal taste and playstyle plays a bigger part in this), it does point out who's more likely to win matches at a high level of play. Also, you got to realize that tiers are only viable under a set environment, in Smash's case being mostly stock mode and no items (along with a few levels being banned due to sheer awkwardness of design, tho 25 of the 41 stages are available, which means only 16 stages are banned and most are levels that nobody cares about (75m, New Pork City, Mario Bros., Big Blue and such)).
Taj is a pretty good example of a good Smash player who sticks to low tiers mostly (his real main being Mewtwo), but who realizes that tiers are still there. He plays most tournaments as his main, mostly focusing on confusing opponents with Mewtwo's awkwardness as well as their unfamiliarity with the character since he's widely agreed to be the second worst character in Melee (due to his awful killing power, bad speed and slow recovery which allows for specific combos to only work on him), but when he gets to the final 8, he suddenly changes tactics and sticks to Marth and Fox. And why does he do that? Because Taj realizes that at the level he's at, if he wants to have a better chance at winning, he needs to do everything in his power to put those chances on his side, and that means dropping Mewtwo for a character who doesn't need to work as hard to get to the same result as the other characters. He'll still stick to his favorite most of the time, but he will switch to something with a bit more "oomph" behind it when he needs to.