Who exactly decides Award availability?
 

Since availability changes literally every minute (I called at 11:45 PM--no availability, and then 12:05AM--low and behold!!!), who decides which seats get to be released for free? Some magical supervisor or pre-set computer system?

Isn't that David Spade's job? ;)

There are generally pre-determined levels that are controlled through the rev mgmt system. That's not to say that tweaking doesn't happen all the time. Analysts will get requests to open up availability all the time on a one-off basis. If there is a problem that gets enough notice, there can be additional analysis to open up or close down availability for one flight, an entire market, or theoretically the entire system.

I do. "No travel award for you!"

The bean counters.