i'll take a stab at it - if you wind load the wall, the wall wants to bend in, pushing the bottom chord into to building. this would want to pop the top chords out, away from the wall. the rods act in tension, holding the top chords tight to the horizontal 'tie' that is 4-5 feet off the wall, stiffening the wall.

a typical qp truss or kp truss loads the bottom chord in tension (assuming no load transfer from a loft floor, etc), or in bending a bit in a qp, where the qp's might load the bottom chord. in this instance the wall is being loaded, and the bottom chord being pushed up into the truss, which wants to pop those top chords open.




larger image:
https://lh6.googleusercontent.com/-rVbl5...10.21.31+AM.png