Zones are used for the light commuter rail service that connects to counties external to city limits.
Inside city limits, the distances travelled are so compressed (even interborough), that most trips are less than ten minutes of actual train ride.
Once you start dealing with zones, you also have to start operating on fixed schedules. The New York City system does have time tables but they don't really operate to the minute. The listed times are mostly just targets. More important is the frequency of trains, back to back trains (double capacity) with five minute frequencies during rush hour, and graveyard has 20 minute frequencies, everything else aims for ten minutes between each individual train.
Again, most people are travelling less than 45 minutes on trains set for 30MPH speed limits.
Hong Kong is significantly smaller than even Manhattan and still employs distance-based fares quite successfully.
I can go from my local station to the CBD (2 stops, around 5 minutes) and it costs roughly US$0.60; another 5 stops on the same line to get to my favorite restaurant bumps the journey to about 12 minutes and costs me ~$0.90. Crossing the harbor from Hong Kong island to the Kowloon peninsula takes less time but actually costs more (almost $1.50) thanks to tunnel fees.
On a side note, public transit timing is one thing that has been irrevocably ruined for me by living in HK. On my usual travel routes the train frequency is typically 2-3 minutes and during rush hour it’s on the order of 30 seconds - the next train often enters the platform just as the last car of the previous train leaves. Granted it does shut for a few hours each night, but even the other top Asian metro systems can't match it.
When I used to spend a lot of time in NYC (before moving to Asia) I had no problem with the subways; now it’s a significant consideration for me when thinking about moving.
I think that the gap between trains and the number of trains per hour is different. I can believe that there are sometimes merely 30 seconds between trains, but train frequencies don't really exceed, let's say, 50 trains per hour (and this is being very generous) because of a combination of signalling constraints and the need to reverse the trains at the end.
You're correct, but this is a mostly academic distinction on a network like Hong Kong's. The gap between trains is a much more important human metric, and it changes based on where you are in the network.
An example: you could fill as many trains as you could physically fit on a track coming from Central (the CBD) during rush hour; a train every 30 seconds or so is crucial to keeping things civil on the platform. As you get farther from Central, utilization falls until you reach a terminal station, where the time between trains can be more like 2-3 minutes without any problems. Through clever signaling you can achieve a much higher perceived throughput on the busiest stretches without actually running more trains.
In the Netherlands all public transport (from city buses you only use for one minute to intercity trains to the other side of the country) use the same chip card. You scan it where you enter the bus/tram/metro/train and scan it where you leave, you pay depending on distance travelled. The buses use GPS to calculate your cost.
It's usually fine for high frequency metros, particularly in peak times with more trains, but time-based zone fares aren't always reliable in other cases.
For example, in most of Switzerland and probably Germany that uses unified zone systems for everything (intercity trains, local buses, boats, funiculars, etc.) the frequency of most train routes is nowhere near those of a typical bus.
Zones aren't usually time based though, they're based on where you got on and how many zones that is away from where you are when your ticket is checked.
Inside city limits, the distances travelled are so compressed (even interborough), that most trips are less than ten minutes of actual train ride.
Once you start dealing with zones, you also have to start operating on fixed schedules. The New York City system does have time tables but they don't really operate to the minute. The listed times are mostly just targets. More important is the frequency of trains, back to back trains (double capacity) with five minute frequencies during rush hour, and graveyard has 20 minute frequencies, everything else aims for ten minutes between each individual train.
Again, most people are travelling less than 45 minutes on trains set for 30MPH speed limits.
(Manhattan is only 20 miles long)