Every page produces a hit and every graphic on the page produces a hit.
A lot of things can cause errors but they are usually from someone looking for a page that doesn't exist or I might produce some errors as I am developing and testing new features for the site. Every connection to the internet has a unique Internet address. If you are dialing in to your ISP, the modem on the ISP end has a specific Internet address. When you hang up and someone else dials into that modem, they are now using the address you were using and would only show up in the log as one unique host. If a visitor returns to our site within 15 minutes of leaving it is still considered one visit.