That's a very good question, and one it would be interesting to know an answer to.
To be honest, I've rarely used this view, probably it's always empty when I log in using LDAP user. But now using rhqadmin I see we there are 1441 suspect metrics the last two days. It does seem to get purged every two days, but not sure where this setting even is?
We have our LDAP user group mapped to the All Resources Role so I would assume this should be able to see this report, I can't see any reason why it should be restricted to rhqadmin.
I see the same in JON 3.3.3 so I assume a bug...