What is the difference between user_status and read_stream FB user rights?

I am confused between these two permissions. From the Permissions Reference, both permissions provide access to the user's message / message. The read_stream permission seems to extend to the user_status permission as it provides access to all messages (means all message, checkin, status ..., as well as a message that adds a user message on the user page).

Can someone provide more information for these permissions? Thank.