We haven't seen the Remans prior to Nemesis. We know that the Vulcans have some psychic abilities and that Romulans are offshoots of Vulcans and that Remans are offshoots of Romulans. There might be a little trickle of psychic ability left in them -- or maybe even strengthened, as a response to their environment.
Also, I read a book by Leonard Nimoy -- "I Am Spock" and he talked about what he was thinking about when trying to create how Spocky should act. He thought that hands and touching were important to the Vulcan people, which explains the "Live long and Prosper" salute and touching each other's heads in a mind meld.
Despite this, the movie still should have explained the Reman's psychic abilities more. Ah well. That was probably one of the kabijillion scenes cut out of the movie.