Well it would be easy to hear them with a desk mic is they actually had no other sound source near it. People will sit multiple feet away from it and it will pick up ambient noise. Besides if you have the volume calibrated for people with headset mics it rarely is loud enough to easily discern people's voice from a desk mic.
I would also disagree with all mics using decent quality. Any cheap bluetooth mic has terrible sound quality (see this all the time when using my PS3 since the system has built in bluetooth).
that's bluetooths fault, not the mics