Hi Paul ,
You wrote above :
"- Kill-cords: I dont really see how a kill cord attached to a lifejacket can come loose if it is secured around a strap. "
True ........but how secure is your life jacket strap or buckle .
Your theory is fine if the kill cord is attached to a stainless steel buckle on a commercial / mil spec life jacket ( which I suspect that you and I would routinely wear ) however many of the lifejackets out there have ( unfortunately ) very dodgy and poor quality buckles and straps .
We always say here in LRPBS that it is ok to attach your kill cord to a strap or buckle if you would also be happy to hang out of a third story window from the same fitting !
I don't know where you get your kill cords ......but I have never in 31 years of driving ( Since age 7 ! )seen a kill cord that would reach my ankles !
There is no way that any one wearing a normal killcord around their thigh or knee can come out of a boat without bringing the cord with them .
I quite agree with testing kill cord switches regularly .
Another dangerous practice which I have seen is people securing their kill cords to the ignition key while driving , which then prevents the kill cord from coming away until the ignition switch breaks or the key gets knocked off allowing the key to be pulled out . I have rescued two such people in my career who ended up " waterskiing " from their killcord half in half out of their boat waiting for the key to pull out of the switch !
Best wishes ,