ALTER USER versus GRANT/REVOKE

Dear PG developers,

beeing used to Oracle, I am a bit confused by PG's SQL support for user rights:
Rather than with "GRANT createdb TO user" user rights are set via "ALTER USER".

Why?

I see the following problems with the current implementation:

a) It is not flexible for future extensions: you always need *two*
   keywords for the ALTER USER statement (CREATETABLE/NOCREATETABLE etc.)
   The User rights are boolean flags in pg_user, this requires changes
   in this table for every little new right (CONNECT, CREATEFUNCTION...).

b) (More important) It does not allow for roles with a user defined
   right profile. Eg. it should be possible for database administrators
   to define a custom group (eg. "developers") with specific rights:

     CREATE GROUP developers;
     GRANT CONNECT, CREATETABLE, CREATEFUNCTION to developers;

Or is there some way to accomplish this with the current implementation?

Christoph Dalitz