So the first time you go to a page, it may count 5 or 10 hits. So everything can change depending on settings I don't control. These in between computers, most commonly proxy-servers, can cache information for a whole group of computers. So in your corporate office, when you load a page through a proxy, it will remember that page. And it also varies by client, and their cache settings, and their browsing behavior.
Some webmasters just lie and make up their hit counts, or have ways of inflating the numbers.
So you can never trust web counts, unless you trust the webmaster. The most common counters are CGI-based counters. CGI's are little programs that load and run on the server. So these are better at getting close. Then they only add to the counter if you are a unique visitor, each day.