wordpress.com stats are based on PageViews. The following are not counted:
* Visits from registered users of the blog when they are logged in.
* Visits to uploaded documents and files
* GoogleBot and other search engine spiders.
See here > http://en.support.wordpress.com/stats/
I have reviewed the ones we can use and you will find links to post on my Popular Posts page under Visitor Tracking. In those posts you will also find definitions and descriptions of the following: Hits, Page Views, Unique Visitors.