so you would rather decide who gets to play who before the tournament draw comes out as opposed to having a somewhat random variation?
the only guaranteed seeds are 1 to be at the top and 2 to be at the bottom. i dont know about other sports, but i doubt other seeds are assigned beforehand in those draws either.
well, the decisions are made before the NCAA basketball tournament (and to my knowledge, every other NCAA tournament) and the NBA playoffs. They are also made before the NHL playoffs, although they reseed after each round. In fact, I don't know of any other sporting event that seeds teams or players and then disregards them when it selects the matchups. The point of seeding is to, in theory, give each player a draw representative of their seeding. That means that, if form holds, the #1 player would always play the lowest seeded remaining player, #2 would always play the second lowest. As tennis seeds it, that doesn't happen.
If they wanted to seed after each round like the NHL, that would make sense (although tennis often has players playing different rounds at the same time due to weather and timing, so that isn't really feasible). In effect, they don't seed at all, they simply group similarly rated players together and then randomly select out of a group. 3 and 4 being the first group, presumably 5-8 being a group, 9-16, 17-32. If there is a 32 player tournament and 1 plays 17, 9, 5 and 3, he isn't really seeded as the number one ranked player.