Oh wow. That's a good point. And my MacBook lights an LED when my webcam's active, but it doesn't for the microphone. Perhaps it should?
http://www.washingtonpost.com/blogs/the-switch/wp/2013/12/18...
Disabling the camera LED is a fairly standard feature in malware suites. Even a lot of USB webcams control the LED from software. The LED is just a feel-good feature.
however the point about the mic stands.
You still shouldn't really trust it, but the situation is not how you're making it sound.
(Doesn't help with the microphone)