Gday and welcome.
^^^^^ That's basically it.
At the moment, the weight of the car is held on the spring mount. This is the load bearing part of the car. Shock absorbers do exactly that. Absorb shock. The mounts aren't made to be load bearing as such. By removeing the spring, and making a coilover setup, you are transferring all your load to the shock mounts. This is where I disagree with the above post, as I believe you will punch out the top first before breaking the bottom mount.
Anyway, coilovers are over rated IMHO. Most people don't touch them once they're setup. You can do the same thing with a good set of shocks and some decent springs.
Edit: I see what you're on about. Those platforms on the outside make the spring seats an adjustable height do they?