Somehow a very American story. Madoff's massive fraud actually enriched some investors--basically, if you invested fairly early, you probably got some pay-offs to maintain the myth that Madoff's funds would be profitable for everyone.
Now the lawsuits are flying. Madoff and his family don't have all that much (although I think they will all be sued, and that may be one reason one of Madoff's sons committed suicide).
So in the search for assets to compensate victims, lawyers have focussed on those investors who actually profited. The argument is: it was all a fraud, whether successful investors knew it or not, so any assets/profits should be divided equally among victims. The counter-argument: how can innocent people be treated as if they are guilty?