The featherweights are far more easily and safely to manipulate than the heavyweights, hence more leeway is possible there. Besides, the rules do not say where the access to the bottle should be.
As a tech checker myself I would prefer to see all safety features neatly stacked together for the arena marshall to handle after the fights, but as long as everything is clearly indicated, as per the rules, I do not see the problem. Unless the marshall has to go to ridiculous lengths in order to access them.
The rules state that the removable link has to be accessible outside the reach of the weapon, but they actually do not mention the same for the dump valve. They only say that the DV should be accessible from outside the robot. Yet, commmon sense dictates that it should be positioned outside of your weapons reach.