In terms of competitive play, the tier list is quite accurate. It speaks of all of the trends and traits of the past few years of competitive tournaments for Brawl. If you've every played Brawl competitively, you would know that unless you were really good, anyone playing Meta Knight had a pretty good chance of completely dominating you. In fact, Meta Knight has been considered a few times for a ban from competitive play. He's that annoying to face. However, a character such as Snake, which is second on the list is also very difficult to face. However, that is only true of the person playing as Snake is very good at the character. Snake requires a lot of skill to play, and a lot of situational awareness. But believe me, watching an excellent Snake play is an amazing thing.
As has been stated in this thread, many people believe that any character can win, and that it is based on the skill of the opponent. While I believe this is true to a certain extent (casual play), it does not apply to competitive play in most situations. Once you get competitive, everyone is really good at the game. At that point it comes down to a concept known as Balance. That is how evenly matched the characters are. A good fighter will have as many characters as possible completely balanced, so it is all up to the skill of the player in a competitive match. However, Brawl has some serious balancing issues. Characters like Meta Knight, Snake, Diddy Kong, and Falco can absolutely dominate most other characters, no matter how good the other player is. If both players of equal or similar skill level, then it is not longer the skill of the player, but the effectiveness and weaknesses of the character. That is why the developers of fighting games try to make all of the characters as balanced as possible, so that it is fair for the people who are playing the game.
Now, I've played in a competitive Brawl tournament, so I've seen all of these things first hand. I often play as Peach in a competitive atmosphere, even though I prefer to play as Jigglypuff or Zelda when just facing friends. This is because Zelda and Jigglypuff are very low ranked, and are not really competitively viable against most of the high tier characters. However, Peach is mid-tier so I can at least get away with playing as her. The bottom line is, the tier list is strictly for competitive play. When I play Brawl with friends, as I often do, we don't follow the tier list or use competitive rules. We just play to enjoy ourselves. That's not to say that you can't enjoy yourself in a competitive atmosphere, but I believe you get my point. When playing with friends, if you don't want to follow the tiers or use competitive rules, then don't. The choice is up to you. That is one of the beauties of Smash Bros.