Site Usage Analytics - Why are figures different for New Posts and can you get more than 7 days data

Hi,

I've been asked to why the number of views on some posts are different to those that are seen in the Site Usage page > Site Usage analytics
I know they are only showing for the last 7 days so if the post was added after this the number could well be different.  Is there a way I can see totals that are current and up to date.

 

Also what is the definition of  Page Viewers and Page Views, and Unique Viewers and Visits??