The tier list indicates match-ups in that the higher characters usually have something that makes them high tier.
mhm. Fox's top rank is based off of how he can infinite you if you even miss an L-cancel. if Fox is played at his absolute meta-game. it is impossible to beat him. whether you were mauled by shine-spikes, infinites back and forth and finished off with an up-smash (if you slide, that is), or constantly juggled to the point of no return. compared to the other characters, hardly anybody has a reliable way of stopping these three things (there's more but these are the main ones).
he can force you to come since he has blasters an well lest you take too much damage he can just finish you off with one-smash if you refuse to come. even if you're Ness or Zelda who can reflect, they still are forced to approach him because the blaster is just too fast.
these are the things that make him top tier. the things in which if done perfectly, he is impossible to probably KO, but like I said, no human is perfect, and therefore, the tier list is merely an outline of who has the most advantages in the majority of the match-ups.
match-ups are single entities that only mean 1/26 in regards to the tier list. Fox is higher than Marth but Fox vs Marth is relatively equal. Fox is only ranked higher because his advantageous are harder to counter IF played perfectly.
yes, I may sound like I'm repeating myself, but in short, "character match-ups" and "tier list" shouldn't be grouped together.