I think this happens because normally IIS has its own processes to access files and Windows 2003 doesn’t audit <i>IUSR_xxxxx</i> and <i>IWAM_xxxxxx</i> users.
Try and change the access information to that file to another user with not too much privileges and try again; this should populate your logs with audit information.
Anyway if you are doing this for monitoring purposes this isn’t the recommended solution.
A better solution would probably be to include some code within the website file which logs into a database and logs the hits there.
You could also setup the page to send a Microsoft Message Queue message so that if the database is down the data is still logged. This would require that some software be written to read the queue and process the data within the message.