Normaly on Vbulletin only MODS and ADMIN can lock threads
( I mod on a non photography site
)
If your on sites where you can lock, delete, edit or otherwise have thread control then you've been given extra rights.
I am a member of a number of sites and they don't allow that in most cases.
The one that gets me is the unusual NEW POSTS system used on Pixalo which I've seen nowhere else.
Suppose it's horses for courses and as I like this site I go with the flow