User blog comment:StrategicMagic/AFK and Disconnect - There is a Difference/@comment-5151680-20121012032906/@comment-216.36.26.248-20121012090042

If I say nothing, alt tab out of the client and kill it via Task Manager, there will be no visible difference on your end between me "leaving" and me "disconnecting".

Not all disconnects are innocent. And not all long-term disconnects are intentional. It's a very grey area. Without any way of knowing for certain whether the person ragequit or is having internet issues, there's no way of clearly telling.