Unregistered people love to use the quick reply box. Back when I had it on my blog-type forum, there were 15 to 30 replies per post.
Now (after updating to 3.6.2) without the quick reply box, unregistered people rarely reply.
According to vbulletin, if I want the quick reply box for unregistered people I have to get a custom hack:
http://www.vbulletin.com/forum/showthread.php?t=206186