How Does a Wired AND/OR Bus work
"However when a device attempts to use the bus the line will be pulled to 0V."
That's it exactly: the bus is high only if all devices set it high. Just like in an AND gate the output is high only if all inputs are high.  

Tri-state logic is not the way to control the bus; if one device sets it high, and another sets it low, you have a short circuit. Usually there's a passive pullup, which keeps the bus at its high level. Each device controls an open drain FET to pull it low.
Like you said, in this setup there's no way to determine how many devices are pulling it low simultaneously.  

This is indeed active high logic: for the AND function the bus is active (high) if all inputs are active (high). If a device pulls the bus low it's just putting a low level on it.