Based on my personal experience now with the Jabber Servers, I have reached the conclusion that it is cleaner to delete the spool files (user.xml) than to muck about with the Jabber protocol in this case.
In 1.0 Jabber Server's you can use the method I originally coerced out of the protocol. However in 1.2 this methodology is politely ignored.
Also, the 1.0 Jabber Servers would never completely kill off the old file anyway.
To this end, release .8.5 will implement a new methodology for unregistering users.
I was a little slow in catching these up regarding the http refreshes, because I didn't have a lot of admin's using this capability. However, it's time has come and it now has all the features of the RegisterUsers class starting with release 0.8.4.1.
Because of the ability to use configuration parameters, whether they be from Config.java or from jabberhttpservlets.config (if you have compiled with CONFIGFILEFLAG = true), you don't necessarily have to include all of the parameters.
For example, when unregistering users you could leave jabberserver, jabberhost, and resource off of unregisteruser.html.
The Jabber Servers have rate limiters, so if you try to run a single servlet at too high of a pace, you will kill your connection. I have written some Java programs to register 100000s of users at a time ... (sorry can't share that ...) and if you find yourself doing something similar, I recommend temporarily turning up the rate limiters.
In 1.2 Jabber Servers you will want to turn up your karma.