They indeed have them on the Metro but they're also installing them on the mainland station as well (you won't be able to get onto the concourse without a ticket). When we were there they were installed but not in use. As they're moving to the OV-Chipkaart now and I guess they're there stop people riding the train for free to the airport etc. All the other stations on the NS network just had card readers.
That will be a pain at Amsterdam Centraal, as many appear to cut through the station to reach the free ferries at the back.