Yes, there's actually a bug about it. ;-)
http://www.virtualmin.com/bug-tracker/bug?bug%5fnumber=15&f%5ffix%5ffor%5fversion=This one of those stupid permissions issues I mentioned a couple of days ago when we were discussing the Forums lack of post editing. Much like the forums, that have the features you want and don't expose them (and provide no obvious way to expose them) to users, the bug tracker provides no easy way to expose commenting to users.
However, I have an OpenACS guy that actually understands how all of this stuff works now...so as soon as the stuff I've already got him working on is finished (tonight/tomorrow is the ETA I have on that) I'll direct him to these little permissions stupidities.
