Rogue,
         I may be wrong here but,i think the tv companies were more thrifty in those days,it maybe stemmed back to the early days of sitcoms (50's & 60's) where recording tape was valued much more than it would be today( tape was very expensive) .Multiple "takes" were not an option in the early days."Hancock's half hour" (tv show) is a prime example,Tony & Sid's mistakes are there for all to see,i think this attitude towards recording shows maybe carried through to the 70's? I'm sure Phil can help here..........