And there are still effects you can't get from rails as easily as you can plex.
For example, I'm building a big Trek style ship and the back has a hemispherical shuttlebay door. I want the door to split down the middle and then rotate open, but the rail system needed to do that and store the segments out of the way would be massive. Or I can simply make a cascading pulse through a series of activators assigned to slivers of the doors so that one button press makes pieces of door open in sequence to get pretty much the same effect in much less space.
Or in the station I'm building, I have a rail elevator up into my bio-dome area. Just comes straight up out of the ground, but if anyone is up there while the lift is at the bottom, I don't want a gaping hole in the floor. So I built a little gazebo over the hole and worked some logic into the rail to activate plex/glass doors that seal everything off whenever the lift isn't there.
Doors and Rails have different MO's, and are useful for different things.