I understand what you are saying . This is a puzzle.
The URL requests should all come into IIRF. If you get one, you should get them all.
I have never before seen a case where you only get "some" requests.
Let me ask, have you tried with other extensions? page.php? page.jsp? Are you able to get
any "no match" queries in the log file? Is it only .asp extensions?
Have you looked at the priority of the ASP Engine in IIS manager?