Let try to explain it in fb terms

DT is just a "friends list"... friends you trust the most
    - Now if you don't have your custom friend list, then theymos gives you one that's DT list
    - Their special capability is they can put a "red flag" on you, if they you try to break anyone's trust (it's not moderated and purely speculative and based on someone's personal judgment)

Moderator
     - Their special capabilities includes moving/editing/deleting your posts or topics
     - They can ban you or lock you out

Staff
     - Same as moderator, but working overtime out of their assigned (board / area)

Global Moderator
     - All those capabilities of a moderator + they can unban you

Administrator: I guess you know it already