Why would an email with this in the header:

X-Spam-Status: Yes, score=13.034 tagged_above=-10 required=6.6

Not be moved automatically to the Junk Folder?

If I am reading the X-Spam-Status line correctly, score=13, and required to be spam is 6.6.. so why do I have to mark these as spam in my inbox for them to move to the Junk folder??