I don't think he wants to go too deeply into religion or risk having to discuss his differences with his church - something that's a no-win for him.
There are some hard core Catholics that won't vote for him because of his disagreements with the church, but those people set their posistion long ago. Most American's are more irritated with the Catholic church then Kerry for their political stance against him.
Most American's are closer to Kerry's posistion on abortion then the Catholic Church's. And many are aware that the church leaders are being very selective in condeming Kerry for abortion but not Bush for the death penalty.
But most importantly, Kerry's talking about religion in a non-denominational way comes across well. Kerry is obviously speaking about something he does believe, and is able to get is some hits on Bush by quoting the bible.
Jay