You can setup snmp traps to alert you to these and many other types of events. In the web interface click on Management then SNMP then set some trap recievers and then in trap controls you can define what you want traps sent about.
Alteratively you can configure syslog in Management -> Logs
I see traps being sent to a trap receiver when I unplug an access point. You should see the trap if you run a show traplog on the cli of the WLC also. If you see that and your monitor tool isn't seeing that trap, then sniff the traffic on the WLC ports and see if you can see the WLC sending that info. I'm currently testing on v8.0 of the code, but depending on the code you are running, you might be hitting a bug.
I have the same AP traps defined as you. What I did was download this free SNMP Trap Reciever to see if traps get sent to that and see the specific OID. Resetting the AP and unplugging the AP did send an snmp trap to the trap reciever and also show traplog showed the AP dissassociation and re association.