I have experienced traveling in the metro system in Australia, US, Taiwan and Japan, and it seems to be that the amount/level of detail is ranked as follows:
US - PA system announces or displays the next stop
Australia - In addition the PA system announces which door (left or right in the direction of travel) opens
Taiwan - In addition there is a display above the door that indicates that it will open at the stop
Japan - In addition there is a display above the opposite door indicating that the other door opens at the stop.
Is this just a cultural thing in Japan and is this really for the benefit of the locals or the travellers?
Extra note: In Taiwan there is even a timer that counts down pretty much to the second when the train will pull up at the stop. Seems almost magical, but doesn't stop people from rushing in and out of the trains in a mad dash that is typical of the metro chaos.
Another note: There were some comments about the number of languages used in the announcement. The most I have heard is three in Japan, and also for signs at airport I have seen four in Japan (Chinese, English, Korean, Arabic).