Ok, got it now.
When central heating first started to become popular, "drops" were often placed behind curtains. This managed to hide much of the pipework. I guess they intend the principal "flow & return" circuit to run in the ceiling void, then drop to each rad.
Jom's right about the mess, but chasing them into the walls (covered channel which is then decorated) is one of the better ways of "losing" pipework. This would need to be done for each rad.......... except where rads can be sited "back to back" on opposing surfaces of the same wall. (Pipework simply passes through wall to the other rad.)
An alternative to this, which I try to use where possible, is to create "boxed skirtings". Simply make up hollow skirting boards to provide a space for heating pipes; hot water pipes; cabling for sockets. Suitably insulated from each other).
With some planning, runs can be dropped inside a cupboard where they aren't seen, then taken through each skirting. Crossing doorways does take some thinking about though.