On the other hand, for most of us of reasonable fitness (able to pass a flying medical for example) I imagine it wouldn't be all that hard to learn to swim effectively - it seems a bit defeatist to say 'I can't swim' and leave it at that.
No disrespect intended to anyone who can't manage it for some physical reason, but surely it makes good sense for an inexperienced swimmer to boost their own odds of survival by getting a few lessons and hitting a pool somewhere for some personal training.