Did you actually read your own links? Yes, they do use the informal term "Sit bones", but neither of them assert that support of the bones is the only factor, and one explicitly denies it.

From the bikefitadvser link:

• sit bone width, torso angle, dynamic motion of pelvis, and surrounding soft tissue all play a role

They both note that width of the saddle will vary with the position of the rider. Unless they've managed to somehow test all sizes and shapes of butts ("soft tissue") with all possible postures, I'm not sure how you can absolutely generalize about whether springiness is really going to cause problems for everyone.

Like I said, I tend to believe people when they say they're comfortable more than I believe "experts" claiming that they must be wrong about their own comfort.