A conceptual question

The order of incoming requests in ISA server has 1. Packet filters and 2. Web 
Publishing (integrated-mode) , 3 Routing rules, 4 bandwidth rules.
 
On my ISA Server, IP packet doesn't have any rule allowing or denying web 
publish.
I know that by default , all is denied if it hasn't explicited allowed.
 
then, Why packet filters aren't denying web publish  ?
 
Alex D.

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