lucy24 - 8:54 am on Feb 14, 2012 (gmt 0)
You don't need a 404 page. That's just a piece of paper. So to speak. The 404 error takes place regardless. Same thing for 403. Even if something goes wrong and the server can't display your 403 page, it's still a 403. It doesn't turn into a 500.
I don't believe robots even see the 403 or 404 page. They just note the error and move on.