The real flaw in the USCG logic for calling the search off is the 20 hour survival calculation. Someone must have assumed they did not make it into a liferaft - an assumption which is hard to understand. The info that the PLB's that were used were switched on in sequence, i.e. one until it's battery failed and then the other, suggests they MAY have made it to the liferaft which surely, given the ingress of water, would have been prepared for immediate use by such an experienced crew.
Keep searching guys....