Syntax Error for "boolean('value')" Type Casting

PostgreSQL 9.0.3, compiled by Visual C++ build 1500, 64-bit

The following intuitively valid statement fails:

SELECT boolean('true')

>>SQL Error: ERROR: syntax error at or near "("

>>LINE 1: SELECT boolean('true')

>> ^

The following work as expected:

SELECT bool('true')

SELECT 'true'::boolean

SELECT 'true'::bool

SELECT bool 'true'

SELECT boolean 'true'

SELECT CAST('true' AS boolean)

SELECT CAST('true' AS bool)

While I'm here.is there any downside to using the "type(value)" form of
casting versus other forms? The main place I will be using them is in SQL
Select statements stored in textual form with parameter placeholders. The
software I use for development allows parameters in the form of ":paramname"
as opposed to the limited "?" so using the "::type" cast form is difficult.
The "CAST( value AS type)" is too verbose for my liking and the "type
'true'" just looks wrong to my eyes - not a huge fan of function calls that
do not use parenthesis.

A sample full query form would be:

SELECT * FROM table WHERE col1 = boolean(:value);

I can replace the ":value" with a "?" before passing it to JDBC (or with a
hard-coded value within Java if so desired) and can use it as-is within
PostgreSQL Maestro.