David,
I think what Avi meant was that if you take full routing table and
not using default, chances are that no matter how many backup providers you
have, you are still risking dropping packets on *YOUR* router if routes to a
particular location are lost. This makes you look bad when your customer
traceroutes.
If you have default then even if all the external routes
get lost you can still deliver the packets to your provider and let him
drop it. This looks favorable from your customer's traceroutes.
In practice, it is better to drop it as early as possible because
any additional delivery is unnecessary, but...
Jun