Bernard,
The technology has changed; new CMOS sensors have highlight shoulders, by dint of adaptation of the well-known anti-blooming technology - furthermore these shoulders seem to be set in firmware. Of course the shoulders mess up the highlight color rendering because they are ... nonlinear
On the bright side, the shoulders prevent totally burnt through holes on cheekbones foreheads and noses on every selfie.
Of course the old CCDs used in MF are linear. I really wish you were right and we had linear sensors and good color in the newer cams; but the trend is to more convenient so...
for CMOS here are some random numbers I made up for you
1.5 stops of the official ISO get chucked in the hilites (non linear, screwed up color reproduction at best). My friends say it is 1.3 stops.
2 stops get chucked in the shadows (read noise, amp noise, readout defects, miscalibration, banding)
1.5 stop gets chucked by moving to ISO 400 so you get a decent shutter speed, handheld
0.5 stops easily are lost to unbalanced light, more in incandescent hence the blue channel noise
so in real life your 14 stop dSLR camera shooting flowers handheld @ISO 800 in incandescent lighting has become an 8.5 or 8 stop camera at most. Talk about DR - ROTFL.
DBs may actually do better because they get used on tripods, closer to native ISO, in balanced light, have linear ceilings so you can use the ceiling DR if you expose VERY carefully, and hopefully accurate readout calibration.
As for urban legends, well some are true, some aren't, depends on who is doing the drinking and talking, but I'd say that when it comes to camera DR and the shooting of Kennedy anyone can have an opinion, orthodox or not, that's ok as long as they're happy about it.
Edmund
Urban legend live long...
There is no such thing as highlight DR with our CCDs/CMOS linear sensors. Be it on backs or DSLRs.
You've only got ISO over rating with backs that result in systematic underexposure by up to 2 stops at ISO100 (Phaseone backs example). I believe that this is were the impression of highlight headroom comes from, it can easily be emulated by dialing in a 1.5 stop underexposure on the D800.
Cheers,
Bernard