I’d be very careful about making this assumption. There is always bleed over in unexpected ways. When these stocks spiked on Wednesday the market as a whole came down hard. Perception is extremely important and if people start to fear that brokerages could be insolvent or just lose faith in the valuations of stocks as a whole it could definitely effect the entire market.
I follow the markets, and the market does a hard mini-crash about once every two weeks. You don't notice it as a buy-and-hold investor, but it raises the hackles of many short-term traders.
