I have only been using the program for a little over six years, so I'm a relative novice at this. But, the Network Shield does not check for viruses period, that isn't its function. for every external link in a web page the network shield will check that domain against its malicious sites list, not the word domain it isn't scanning for viruses.
I suggest you spend some time browsing the viruses and worms forum you will find this to be correct.
Or from practical experience the network shield would alert before the web shied has a chance to even scan the page content (note the work page, which includes imports into that page). So if the network shield doesn't alert there should be nothing wrong with the page content, wrong as the many cases of the web shield alerts in the virus and worms forum attest.
If the network shied was scanning the page content the web shield wouldn't get a look in and would be redundant and that clearly isn't the case as they do different things.