Why does pgAdmin3 set OIDS=FALSE and owner to postgres by default?
1 Why oids=false?

OIDS=FALSE/TURE,  the default setting depends upon the default_with_oids configuration parameter，The parameter is off by default。in PostgreSQL 8.0 and earlier, it was on by default.

2 Why ownered by postgres?

Please check the role you use log in  when using  pgAdmin3 ， if you log in as postgres role ,then  the owner of  new created table will be the postgres role.