Holy cow! Now I think this is my favorite build of yours so far. I dunno. The 6x6 was pretty epic. I wanna come play with your trucks, that's all I gotta say man. Nice work!
The spring doesn't limit the travel, the shock shaft does. In those two shocks, they are different size springs. I am guessing the shorter, smaller diameter one is a lot softer spring.
Basically, with full droop, your shocks are 'just' fully compressed by the weight of the vehicle. When a wheel goes over a lower piece of terrain, the wheel drops down and a little spring pressure help push it down.