Quote from Capablanca:
SIPC is there to protect all investors covered by it. All these other investors are hurt when it is asked to cover claims it isn't supposed to. On the other hand, if there is a legitimate claim they better cover it or it will be shown to be useless protection.
What I am not clear on is whether Madoff's fund qualifies as an entity that deserves SIPC help. With a fund there is an explicit acknowledgment that returns aren't guaranteed and that you can lose all your funds. That isn't quite the same with a brokerage account the money in which one does not expect to be put at risk unless directed.
I have zero legal expertise in this matter but my gut reaction is that they should be covered up to 500k if they had an account with the brokerage and they lost stuff due to its collapse that they otherwise wouldn't have at another brokerage. If they lost money because of the collapse of the fund, however, it should be tough luck not a penny back.