This had two benefits: 1) you could tell if you were going to get a spot in/near centre-ville or wherever you were going. 2) you could tell if it was likely you would find any spots - if all the garages nearby were at/near capacity, you probably wouldn't find parking on the street either - be prepared to park further away and walk.
This was possible because of government control of parking and signs - the city itself (not to mention the residents) benefited from lowered gas usage, less congestion and less frustration. Thus it is economics/government as much as technology.
Coming from Houston I wasn't used to something like parking being so well organized. ;)
Westfields Bondi Junction went as far as having an iPhone app where you could put in your car's license plate and it would tell you which spot it was parked in; that caused some privacy concerns and I don't know if it's still available but the technology exists, and presumably the cost is offset by the extra metrics you get by tracking every single vehicle that uses your shopping center.