Shouldn't ON UPDATE/DELETE triggers be BEFORE triggers?

While thinking over Jeremy Radlow's recent problem report in
pgsql-general, it occurs to me that it's probably wrong to implement
referential integrity actions like ON CASCADE DELETE in AFTER triggers.
Seems to me that this breaks the fundamental rule of referential
integrity: if B references A then there must always be a matching A
row for every B row.  Therefore, if we delete a row from A we should
delete the matching B row(s) before, not after, we delete from A.
Otherwise the remainder of the transaction sees an illegal state of
the database.

Comments?  How about ON UPDATE actions?
        regards, tom lane