And why DO planes carry life jackets ???
Anyone who has ever belly flopped off a diving board knows how hard water is.
Planes don't "put down" on water (as described in the safety announcement).
A plane "putting down" on water, from 30,000ft up, will simply disintegrate.
And, unlike in the movies, a commercial airliner does not glide down and skim along the surface of the water. It would be ripped to pieces.
The best thing to do if a plane is in trouble is to adopt the well known "brace" position. At least that way, when the plane crashes, your neck will be snapped by the back of the seat in front, and you will die quickly.
Oh, sorry, Carl. Err ... did that help at all?