Haven't seen this mentioned yet:

Tourists swim 14 hours after boat sinks

I'm curious what others think, since it seems that the people that didn't follow what I thought were the general rules (stay together, stay with boat) ended up surviving better.

This may simply be an example of the fact that chance plays a role in survival just as judgement does. You can do everything wrong and end up OK, and you can do everything right and not survive.

Were the survivors just lucky in this case? Or is there an argument that they made the right decision to swim for it?

I have a sense that these two were much stronger swimmers than the article mentions. Generally staying near where the mayday call would have SAR looking is the thing to do, but so is having survival gear and being dressed for the environment. Since there was no boat or liferaft to stay in, if you are in the water you may as well go for it.

There's a reason PLB's are waterproof.

They apparently had no signaling gear either with them or attached to the floatation. That would have made a huge difference. Everyone was very lucky, all around.

They were very fortunate to be in warm water. Their life expectancy off the coast here in southern California would have been about an hour,unless they would hve been wearing wetsuits; their are cases of wetsuited survivors lasting for more than 24 hours.

They were wearing lifejackets by the time they were in the water. She was wearing a swimming costume and a sun-dress, which sounds appropriate to me. They abandoned most of their clothes to swim better.

It sounds like they got to land after 14 hours, and the crew got rescued after 23. It also seems like they could see land when the conditions were right. If I could see land, I'd find it hard to resist the temptation to swim for it. It's hard to spot people in water; they mention a helicopter missing both them and the crew.

In my opinion they were extremely lucky. The usual advice to stay together and stay with the boat is appropriate in almost all cases (exception noted below).

The article indicates captain had managed to send a Mayday with coordinates. It is very difficult for rescuers to spot people in the water from the air or from another boat, but a group of four people is always easier to spot than one or even two people. Also, even if the boat sinks there will usually be some amount of floating debris that also aids spotting by rescuers. Perhaps had they all stayed together they might have all been spotted sooner?

As noted by hikermor, cold water is also an issue. With a life jacket, by remaining still and huddling in a group you increase your survival time. When swimming, you usually cool quicker. Even though your muscles put out heat from the exercise, you are constantly flushing cold water over your body. The net effect is that in most cases you cool quicker.

Note that "Soon after, they also lost sight of land amid the rain." They could as easily have ended up swimming away from land rather than towards it. Also, even a slight amount of current could have carried them further from their destination.

All in all they were extemely lucky, in my opinion. About the only situation where swimming for land might be the best choice is when there is little or no possibility of rescue. If you are out by yourself, in a seldom traveled area, and left no word with anyone about your plans so no rescue will be launched, then it might make sense to swim for it. Otherwise, staying with the boat is the best plan.

There will always be a few lucky exceptions, but almost always you have better odds staying with the boat.

Per http://www.surf-forecast.com/breaks/St-Lucia/seatemp, the water temp off St Lucia was about 77 deg F. as I read the chart. What's the survival stats say about survival times in 77 deg water?

The best I can come up with is a small scale graphic on page 11 of [/u]The Survival Book[u], authored by Paul Nesbitt, Alonzo Pond, and William Allen, 1959. The chart reflects February conditions, and indicates that the victims were in Area F, where the survival period is indefinite and excessive fatigue is the more likely cause of death. Per their map, if you fall overboard, best do it in the tropics, not on the west coast.

If memory serves, Dr. Giesbrecht defines cold water as anything below about 20 C (68 F). Survival time (with floatation) varies a lot, depending on body mass, gender, water temperature, etc. See the graph at http://www.coldwaterbootcamp.com/pages/1_10_60v2.html

In the case under discussion, water temperature clearly wasn't a major issue. The mere fact that they survived in the water for 14 hours demonstrates that. However, most places outside the tropics don't have water that warm. For the general case, water temperature is often (or usually?) a significant issue. Water that may be warm enough for a short swim could be lethal with long exposure.

Essentially, at 77 deg F, hypothermia is not going to be an issue.

77 deg F is 25 deg C, and this chart shows 30 hrs to indefinite for that temperature, even naked: Survival Time in Hours in Cold Water

For colder water, body fat and clothing are big factors - see:
PREDICTED WATER IMMERSION SURVIVAL TIMES FOR ANTI- EXPOSURE ENSEMBLES

This seems to be a good site on the topic: Cold Water Survival

Interesting site. Thanks, rafowell!