Denabol, forgive the speculation on my part, as I wasn't there to witness it...
but I would hazard a guess that the egress of these pax would have been a little slower than planned for due to the proximity of boats and land... in an open water ditching, if the water were that high in the cabin, it would be a case of get them out in lifejackets and worry about the rafts later... pax can always jump and swim to a raft if need be. So probably would be much faster if immediate rescue wasn't in sight... who knows the flight crew might have had time to make an announcement of the sort if they saw boats close by before ditching...
Yes a scary situation, one we train for in the (cabin) sim and yes even in practice strong assertive tactics are required. It's a matter of asserting your authority as the trained professional and if need be, use a willing able bodied passenger to assist you to keep those doors closed... heck, tell them it'll sink faster once those doors are open if it keeps them away from the back! It's amazing even a small 5 foot something flight attendant can keep back a bigger passenger if the verbal technique is right, I've seen it done and she might as well have had a bloody big axe in her hand!
Seems that a LOT of factors were in the favor of pax/crew today, one or two things different it could have been a much sadder outcome (Air Florida as mentioned, which was my first thought on hearing the news bulletin!)