The bugzid to build a link is really useful. It would be complete if the bug being referenced had a list of the bugs that refered to it.
Unfortunately this feature is just a shortcut. When you write BugzID:32 it stores that as normal text... but when it displays it to you, it recognizes it and adds the link. So its just a text substitution - there isn't any database state to go along with it which would allow a bug to see its referrers.
Michael H. Pryor
Fog Creek Home