interval and timestamp change?

this works on  postgresql 7.1.3.

SELECT interval(('1/30/02  12:30 pm'::timestamp) - 'now');

However, it is failing on the current beta. I have to change it to:

SELECT ('1/30/02  12:30 pm'::timestamp) - 'now';

Is this change to make PG more ANSI compliant? Was this 
documented? It  took me a bit of hacking to find the correct syntax in 
7.2.

Ted