Porto have been kicked out of the Champions League for their allegedly bribing referees...
http://news.bbc.co.uk/sport1/hi/football/europe/7435898.stmAC Milan, who were found guilty of match fixing 2 years ago, were allowed to play in the Champions League, despite their punishment by the Italian FA, and went on to win the Champions League last season.
One rule for one...one for another....
Previously AC Milan were excluded from the Champions League in 2006 following the investigation in to corruption in Italian football that saw Juventus relegated.
But they successfully appealed against the decision and went on to win the competition.
I'm not sure of the ins and outs so cannot pass verdict on whether it's right or not, but I'd say the circumstances MAY have been different. Of course, this is European football so it could be 'one rule for one' as you say