Are they typically the same train but if people change the platform to another train, they would arrive at the destination a bit earlier? - Exactly.
It is one and the same train from Interlaken to Zurich HB to Romanshorn.
The difference is, if peoole change at Zurich HB, and use another train to the airport, they arrive 2 minutes earlier at the airport than using the direct (your) train, IC 81.
Two minutes can matter in the dense Swiss train network, to catch another service.
That's all about it.
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