In my case it was a matter of practice, when I got the D800 I was surprised how many of my shots had camera shake, now 6 yrs later I can handhold at 1/FL and get a decent amount of good shots
I would agree with Armando...
I had the same problem when jumping from the D700 to the D3x. I thought at first that The bigger photosite captor induced a need for higher speed, but in fact I discovered that it was mostly my sloppy (or lazy) way of holding the camera ! I had been spoilt by the D70, D200, D700 with which you could even shoot one handed (and get results).
I trier to compare my use of Kodachrome 25 years ago (or technical Pan), hand held and concluded that in film times (and manual focus), with lesser speeds and big clunky mirrors we did manage to get sharp pictures even a big enlargements. So it had to be something else...
While we do not have here the culture of using frequently a tripod (Cartier-Bresson's era), I do have some old Gitzos and tried them... Perfectly sharp on my D3x ! So I learned again to hold properly my camera !
If I manage to get a D850 (mostly a price problem and maybe a philosophical one) I guess it will be the same effect getting there from the DF, I'll have to learn all over again