This seems kind of odd to me. It's not something you'd find over here, but then in domestic premises in the 1960s/70s era you'd be lucky to find any sort of prewiring like this anyway.
This was still the era of the G.P.O. monopoly, and telephone wiring in residential didn't go in pretty much until the house was otherwise finished and the owner ordered service from the Post Office. Then it was usually just round-sheathed 4-conductor cable clipped around the baseboard.
Even in apartment buildings where some pre-wiring may have taken place, I've never seen anything like this.
Just how much thicker/tougher is the insulation on these wires compared to those within a normal cable?
