Almost 100% sure AVG can't scan a URL/website to see if it has a virus, free has no options like that except maybe a plug-in which could I suppose, I'll check pro at work tomarrow to see if that does. Actually I've never seen anything that could scan a website for a virus, brilliant idea and if nothing does do it someone should do it!
I can almost see it now, a website that you can chuck a URL into and it can search it for viruses/ad-ware/linked to a list of known phishing sites etc.