Brum Royal I was under the impression that relegation issues were decided over a points average over a six "season" (in fact a 3 month) period, and not in the normal way.
It certainly is complicated though
http://en.wikipedia.org/wiki/Brazilian_football_league_system
It depends on the state, I think. Argentina uses(used?) the average system over four half year seasons. River got relegated the other year, hilarity ensued.