It has a unique usage, there is not regional difference.
Actually, it's just a logical problem. Gleis (rail track) is where the train approaches, Bahnsteig (platform) is where the people are waiting.
A train can approach am Bahnsteig 3 or auf Gleis 3, pay attention to am and auf; am means alongside the platform, auf means it goes on the rail track. The station announcement can use both versions, it doesn't matter, both ones are correct. They just should use the proper preposition to hold back people from entering the rail track or prevent the train to jump on the platform, respectively. ;)
Examples to check:
- "Der Zug hat Einfahrt auf Gleis 3!" vs. "Der Zug hat Einfahrt am Bahnsteig 3!"
- Note "Bitte begeben Sie sich zum Bahnsteig 3, der Zug hat Einfahrt auf Gleis 2!" could be used, if platform 2 is closed because of a a building lot and platform 3 is alongside rail track 2 also.
- zu is possible with "Bahnsteig" and "Gleis"; the announcement "Bitte begeben Sie sich zu Gleis 3" expects you know what to do in that case, and you can choose the platform by yourself