Ask HN: Why is iOS microphone notification not active while listening for Siri?

iPhones listen for Siri without displaying a microphone warning in the notification bar.

Only after Siri is activated does the notification appear. This must mean that the notification and the microphone are independently operated and not a true signal of whether the microphone is actually listening or not, no?

Can someone explain how this feature works and why this is or is not an issue?