You can add hardware features in order to support features you want to support in the future, but not advertise them in case those features for some reason don't come to fruition. If they had advertised "contains a microphone" there could be users who claim false advertising if they can't use the microphone. It's stupid but I can see a lawyer making the argument.

As long as the microphone never recorded anything, they're no legal downside to including it and not documenting it. There could be a slim but potential issue with advertising a microphone that the customer can never use.

The response to this incident is showing that that view is changing though.