Sure, 20Mb/s is at the very top of the scale. Out of all the people I know with broadband though, only a small handful have 5mb/s or below, and all because of their extreme distance from the exchange - the bulk sit at 7-10MB/s or above. Anecdotal but hey....fact is, 3Mb/s or below is unacceptable in the modern world - as Maestro's moving house sentiment expresses.
Thankfully, such data is trivially obtained. While there is a bunch of comprehensive research globally, most heavy research goes into areas beyond just raw download speeds. Lets keep it simple.
http://www.speedtest.net/global.php
I refer to this because it's probably the most comprehensive and up to date raw data.
NZ clocks in 44th with a residential average of 6.29Mb/s - twice Maestros speed. The US clocks in 25th with 10.38Mb/s.
NZ's internet problems are more to do with high price, poor download caps and limited available international bandwidth, rather than inherent raw download speed issues.
Somewhat related: it's unfair to compare with the traditional broadband heavyweights like South Korea, Sweden and Japan, because they built up their ultra high speed broadband around vastly bigger population densities, intensive rollouts, and the fact that they are monocultural societies whos language is only spoken within their borders, creating massive domestic demand compared to english speaking nations.
A bunch of the other nations at the top of the list rank highly because of how new their infrastructure is and what low penetration they have - i.e. not much of the population has internet access, but those that do have very high speeds.