I track my website traffics using Google Analytics, but for my websites that run on Drupal I also look at the Drupal logs under Administer to see what people are doing on the site. I've noticed that the two don't agree. Drupal logs a lot more than Analytics does. For example analytics will tell me no one visited a site but in Drupal logs I will see several visits, searches, and referrers from different IP addresses for the same date.
Various things could cause that effect. Goog Analytics will ignore the below. Bots, including search bots, hacking bots, spam bots, email harvesters etc. Users with Java Disabled. Visitors is using something like Firefoxe noscript extension, or a proxy, strips analytic JS, the visit simply can not be tracked by analytics, as can some security products such as norton etc. Referrer spam. Error pages etc etc.
Thanks for that explanation. I guess it makes sense then, because I was starting to wonder what was going on.