The Unique Visitors you are missing here are the ones which came to your site from internal pages (Referrer = Internal as it matches the Internal URL filters) which is called the "Inside your Site" traffic.
To validate the numbers you can pull the Data Warehouse report for the same and you would see a blank line item with numbers for "Inside your Site" traffic. Please refer to the below mentioned article for details regarding the same:
I would not suggest turning off the Internal URL Filters as doing that would inflate your Traffic Sources report. The intent of Traffic Sources report like referrers is to provide the metrics on how well the sources from which the traffic is coming to your site are doing. And that is the purpose we do not show "Inside your Site" traffic in Referrers report.
I hope this helps. Please let us know in case of any further query.
So that means the largest proportion of my customers from "Inside your Site" traffic? How can i know where they come from before get into my site? and How can the chart show the field "inside your site"? Thanks a lot!