Probably because we ride the same train nearly every day, rail commuters seem friendlier than subway commuters. In addition to "train buddies," we also see the same conductors each day, and they see us, so there gets to be a bit more of a bond there.
This morning on our way in to South Station, the conductor came down the aisle as usual. He paused at the seat in front of mine, and looked carefully at the man slouched in it. The passenger was napping. The conductor gently reached down and adjusted something; to me it looked like he dog-eared a page in the rider's book, so he wouldn't lose his place during the nap.