Ultimately what you wear is obviously down rightly to the individual and ones attitude to risk but in any event I'd go back to Sir N D's comment that
A long time ago I tried ditching for real. Knowing it was coming was frightening, the impact worse than I could ever have expected and the aftemath dreadful.
If it all does go mightly pear shaped in an aircraft (over land or sea) it's quite possible that things will start top unravel very quickly, and no amount of training, even the top notch military stuff some of us have endured, can really prepare you for the psychological impact (?shock) of going perhaps almost instantly from a nice warm environment to a world where very much at the mercy of the elements. Being over the sea in those situations, perhaps looking down at the water having had an engine failure or worse you very rapidly become aware that the fact you perfectly handled the initial technical problem is now history, and that you've only just started to confront another whole set potentially lethal problems...
Regardless of whether you think you need the kit, need to wear it all the time etc, the more thinking through of sea survival you have done and the more practising of appropriate procedures you have done, the more chance you've got of surviving a ditching or similar.