Can't use "any" with SQL functions

Is there a reason we disallow using "any" with SQL functions?

decibel@phonebook.local=# create function textcoalesce("any") returns
void language sql as $$SELECT coalesce( $1::text, '<NULL>' )$$;
ERROR:  SQL functions cannot have arguments of type "any"
STATEMENT:  create function textcoalesce("any") returns void language
sql as $$SELECT coalesce( $1::text, '<NULL>' )$$;
ERROR:  SQL functions cannot have arguments of type "any"
decibel@phonebook.local=# SELECT version();

version
------------------------------------------------------------------------
-----------------------------------------------------------------------
  PostgreSQL 8.3.7 on powerpc-apple-darwin8.11.0, compiled by GCC
powerpc-apple-darwin8-gcc-4.0.1 (GCC) 4.0.1 (Apple Computer, Inc.
build 5370)
(1 row)

decibel@phonebook.local=#
--
Decibel!, aka Jim C. Nasby, Database Architect  decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828