from my own experience waitlist clearance isn't "instantaneous", both award and paid, even full fares - if you are waitlisted in a certain fare subclass, even if a seat opens up for that subclass under the POS applicable to you, it might take from a few minutes to a few hours to get the seat changed from waitlisted to confirmed - it's automatic (I think, guess it can't be manual), but not always instantaneous.

and if anyone (even without status) calls to confirm a seat during this time (between the seat opening up and it being confirmed for someone at the front of the waitlist), he/she could get the seat, no matter how many DM/GO/SL/etc are on the waitlist. again, at least that's my experience...YMMV. I have often used it to my advantage by checking availability often and call / have my secretary call immediately when I see some availability; sometimes when I am busy or when the flight isn't important enough, I often see a seat opening up and yet my waitlist doesn't clear until a few hours later.