Functions vs. Columns?????

Hi,

I have a question as to how postgres handles some built-in functions,
for example:

Works                        Doesn't Work
------                       ------------
select now();                select now;
select current_date;         select current_date();

It seems that there should be some consistency here in the use of
parenthesis.  I don't really know how these things are handled on the
backend, but it seems that parenthesis are the more correct way, or at
least both should be allowed.

Any thoughts?

Byron