Electrically there's no problem if you drop the cables down through the wall void as described. The installation method used is more driven by ease/speed for the installer, the robustness of the finished installation and any local regulations for building works and fire.
The method you describe, where metal conduits have been laid in the wall, is typical of cabling that was installed when the building or room was constructed. Once the bare carcass is up the electricians/cablers will come in to do their 'first fix' which involves installing all the conduit, cable trays and containment for the cabling to every required outlet point. This allows the wall panelling to then be installed and the building finished off alittle more bbefor ethe cablers return to pull the cables into situ and add the faceplates etc. Your situation is that of installing into an existing wall so embedded conduit is not really an option.
You really have to choices; either run the cable down the wall void as suggested or if that is too tricky you could run it down the surface using the self-adhesive PVC mini-trunking available from most electrical wholesalers.
Finally; do bear the fire regulations in mind as they may stipulate the type of cable you install. For example, in many countries if you install into a space that handles ventilation air you must use LSOH (Low Smoke Zero Halogen) cable
