IB has their timber hill market making division. Perhaps the $14.5bil in re-hypothecates is what IB uses to provide trading capital for that division.
You must not have read all of the information provided by the link provided by the original poster of this thread.
Saico, be careful. There is prop trading going on at IB. Look over this thread: http://www.elitetrader.com/vb/showthread.php?s=&threadid=230372 In which a company rep discusses just one such trade.
SIPC is NOT federal insurance. In any case it only covers 100k in cash and many full time traders have way more than that at IB.
Yes, with SIPC $400,000 in securities, and $100,000 in cash were the last figures I read about that are covered.