I guess Demoninja covered it. To give a simple example, imagine a 4-person single elim bracket. Mind you, this would never happen cause with 4 people, you'd probably want to round robin, but this is for the sake of an example. In the first round of eliminations, one guy is eliminated from the top of the bracket and one guy is from the bottom half. There is no way to determine who gets 3rd and who gets 4th, so you say that they tie for 3rd. This kind of thing always happens in single/double elim brackets. There are placings that are always ties: 5th, 7th, 9th, 13th, 17th, 25th, 33rd, etc. The only time you can determine a clear 1-8 is when you have people play sets to determine ties. This generally only happens in round robins.