Kiosks can be used by citizens of all VWP countries as long as they have entered the United States once since 2008 via the "normal" process. VWP countries are all required to issue updated biometric passports - even the newest member, Chile, estimates that less than 15% of the Chileans entering the US have the old passports that don't work with the kiosks.

The reason this isn't widely known is because there is very little publicity about the kiosks in these countries, so most of the people who could use them still wait in line, and/or, in some cases, the kiosks are placed in a way that makes them look like they are for US citizen use only.