Are the hardware-based questions are on-topic for this site? As I personally think that this site is for Android OS complexities and not for the hardware on which the OS runs. Have a look on these questions. This and this. They are merely related to microphone and don't have any direct link with OS. Moreover the matter questions discuss about is not specific for Android, as I own a Windows phone with two microphones as well. So, are the questions of this sort are on-topic?
End-user hardware questions specific to an Android device are absolutely on topic.
The first question you linked might be considered off-topic, since (as you said) it's not specific to Android devices. However, we tend to give some leeway when the OP might not necessarily know that and is asking as if it were about Android. The second question, though, is about a specific Android device and absolutely fine in that respect.
(We have debated whether "Does Device X have feature Y?" questions should be allowed here, but that's a separate concern.)