Originally Posted by
AnkleWork
Because it is a tension stayed structure. The tension in the red spokes net-out. The load on the hub is transmitted to the rim via the top spokes. There's a good reason you don't want to see a FBD of the hub.
Also, there must be a reason you use the extreme case of a wheel with four completely slack spokes rather than a proper wheel.
That particular diagram (which I did not create) shows a load that is crushing the wheel. The interesting thing is how the highest spoke loads aren't directly above the hub.
I think you're getting too wound up in the semantics to appreciate the fact that the change in load on a bicycle wheel is, in fact, seen as compression on the bottom of the structure, rather than an increase in top spoke tension.