It's likely an internal microphone and speaker; the sound card may not support input through that interface. What you're saying can be true for many other modern computers, though.

There was an article (a while ago) showing that at least one major brand of onboard sound cards has undocumented features to switch the audio-out jack port to input. Cheap headphone/earbuds function as a microphone too, so that's a thing. Only if you leave the earbuds plugged in, of course. It can't listen from an empty jack port.

I (personally) think that intelligence/privacy-wise the mic on many devices is a lot more troubling than a camera. Camera is very directional and (again, personally for me) would at most result in embarrassment? While a microphone can record all conversations in a room/appartment, transmit everything with fairly negligible bandwidth, and taping over it won't do much good. You actually need to open the device and disconnect/cut a wire.

OT: @lightedman you're dead. Apparently due to some heated discussion on the term regression. But from a glance I couldn't find anything that stood out enough to warrant a ban. Might want to send an email and have your account unbanned.