Roles as objects in Postgres's security system

Hi!
My English is bad, so in short - why Postgres (and surprisingly other's, like Oracle) lacks something like this:

1. What roles who can create or delete (insteed solid CREATEROLE privilege)
GRANT { { CREATE | DROP }
    [,...] | ALL [ PRIVILEGES ] }
    ON { {ROLE rolename [, ...]} | ANY ROLE}
    TO { rolename } [, ...] [ WITH ADMIN OPTION ]

2. What in what roles who can alter
GRANT ALTER { LOGIN | PASSWORD | INHERIT | RENAME | VALID | SET | и т.д. }
    ON ROLE rolename [, ...]
    TO { rolename } [, ...] [ WITH ADMIN OPTION ]

3. What roles who can grant to whom
GRANT GRANT {ANY | rolename [, ...]} }
    ON ROLE rolename [, ...]
    TO { rolename } [, ...] [ WITH GRANT OPTION ]

Any Help Will Be appreciated!