Differences between Server Log and Piwik Log


we have checked the differences between the server logs (awstats) and Piwik. In a period of 6 month there is a average difference of 63%. Piwik seems to track just a fraction of visitors. The website produced traffic of less than 100 000 visitors between the 6 month.

Does anybody else made similar experiences? Why is the difference so big?

Piwik v1.4