Well ... until PG 7.2 PostgreSQL didn't support CREATE OR REPLACE, so it wasn't an option during our first couple of releases. Semantic changes in the opaque type used by trigger functions mean you can't use CREATE OR REPLACE with any of these you want to be able to upgrade across the PG 7.2->PG 7.3 boundary.
And PG 7.2 doesn't support CREATE OR REPLACE VIEW :(
(7.3 does? hope hope)
We're getting *close* but aren't quite to the point where we can CREATE OR REPLACE everything, sadly. But we can do so for normal functions now since we no longer support PG 7.1 I've been switching over some create scripts when I've had other reasons to visit them.
If anyone wants to go on the warpath to do this for any particular package, feel free ... just keep in mind that it's not kosher to use CREATE OR REPLACE VIEW yet or to use CREATE OR REPLACE on a function that is used in a trigger.
Of course if there are any missing REPLACEs on Oracle packages these should be fixed ASAP.
