CREATE OR REPLACE TRIGGER not supported?

Hello all,

A few days ago, I found that "CREATE OR REPLACE TRIGGER"
is not allowed on 7.4.2.  However, functions and rules allow
"CREATE OR REPLACE" statement.

Is threre any reason not to support "CREATE OR REPLACE"
only for triggers?

Thanks.
-- 
NAGAYASU Satoshi <nagayasus@nttdata.co.jp>
OpenSource Development Center,
NTT DATA Corp. http://www.nttdata.co.jp/