There are actually two methods we use to capture the website traffic, and they show different results so it's good to know which one to use and when / why.
First, the counters that show on the bottom-left of the home page are driven by our raw server logs and use a program called SmarterStats to provide the analysis. We extract that data on a daily basis to display on the site, but if there's a hiccup then the counter might not show for a day or more and we'll usually get it fixed asap. These logs will include any visits to the site from any device for any reason - so it'll include calendar feed requests, Google Image searches, etc. So the number shown in the counter will be the "big number" but not necessarily the best measure of human-generated traffic.
Hope that helps,