They don't do it anymore. At least, they're not allowed to.
I ride the Seibu Ikebukuro Line and the Marunouchi Line into work every morning now, and while there are a lot of people in the trains (too many for Western standards), no train conductor ever pushes / forces people into the train.
Japanese people actually are not very polite; they're very selfish and idiotic when it comes to getting on a train. If it's crowded and there's no room, people on the platform still try to force their way in. At the same time, people in the car don't move unless they are pushed, and then they push back to get room. During this brief fight, the doors are closing, so I've seen a few people being pushed back out on the platform.
You know what's scary? The obasans!! Holy smokes, are they dangerous! When I first went to Japan, I went out of my way to be polite and offer them seats, but not anymore!! These obasans are the WORST of the Japanese offenders. They kick, scratch, and straight-arm you out of their way when they get on the train. I've received a few punches to my groin, my liver, jabs to my knees, slaps to my face, etc. just because I was in their way, even if I was there first!!
Oh, the stories I could tell. In Japan, instead of road rage, there's train rage, ahaha...