Well, there are a number of different forces the tripod is subjected to.
Wind, shutter impact, mirror slap, etc. Then the tripod reacts by either absorbing or resisting the energy that is introduced into its structural system.
Harmonics also come into play. The goal is to have the tripod resist and recover as fast as possible.
To have a tripod that is vibrating for any amount of time at all becomes to some degree, an issue.

Here's a real-world example taken on the Gitzo G1228 tripod with the RRS BH-55 ball head. This is a direct crop from the original RAW file. 371 x 298 pixels.

Here's the things that the image had going for it:

A great camera, the D2x
The shutter speed, 1/80th on a TRIPOD!
f/5, a sharp aperture
carefully focused
The very sharp Nikkor 28-70mm AFS
MLU (ON)


So why is it so soft? Its the tripod which was reacting to a breeze; i.e. microvibration. Why? Harmonics and lack of stiffness. I could feel the tripod fluttering in the breeze after the shot... which was very disconcerting.