It's incorrect.
The handlebar is a double ended 40cm lever held in place in the middle by a 4cm clamp. All of the forces exerted at the ends of the bars are transmitted through its center, to the stem, and to the head of the fork steerer. The handlebar doesn't need to be very stiff out where the hands are, but does need to be at the center.Stiffening this region motivated the moves from quill to modern stems, from 1" to 1 1/8" steerers, from 26 to 31.8mm daimeter bars, and the adoption of larger diameter 4 bolt stems. All the modern stems are a vast improvement on what came before. Wider cross section stems make a noticeable difference in how much movement is possible at the ends of the handlebar.
Here's some more reading on a 5 yr old test: http://caletticycles.blogspot.com/20...stiffness.html