I’m writing my doctoral thesis exactly on seeding in playoffs.
First of all, strictly speaking, a system completely eliminating "tactical losing" can exist. I exclude the example given - a case when only one team advances to the playoffs. The system eliminating “tactical losing” is the one where all the teams participating in the regular season also participate in the postseason and the rule in the postseason is a “random seeding”, eg. all pairs can be formed with the same probability independent of the performance in the regular season. Of course, it is unacceptable. It is unfair and all the matches in the regular season are of a kind of friendly matches with no stake.
The important insight from the above example is such that if we allow only some top teams to advance to the playoffs (as is always a case), even a random seeding cannot eliminate “tactical losing”. There’s always a chance that one team will try to knock the other team out of the postseason. I think the match San Francisco 49ers vs Los Angeles Rams from 1988 is a good example here – see http://en.wikipedia.org/wiki/Match_fixing#Better_playoff_chances.
In my thesis I try to minimize the risk of temptations to “tactical losing”. I propose a measure of this risk (it takes into account the number of such temptations as well as their strength). I suggest a new method of seeding in the playoffs. The comparison of my method to different proposals is performed with Monte Carlo simulations.