Shorthand column labels (SELECT col1 foo, ...) vs (SELECT col1 AS foo, ...)

I notice PG doesn't allow shorthand column labels -- it requires the 
'AS' operand.

SELECT col1 foo, ...; -> ERROR: syntax error at or near "foo"

For compatibility with other databases, what objections might be argued 
in allowing this syntax in the future?

On the 'pros' side I think it eases migration to PG, shortens code, is 
similar syntax to shorthand table aliases, and some users might argue it 
has become defacto syntax among DBs.

Regards,
Ken