The Top 10 List, as airgaps and kureshii mention, is a compilation of the total amount of visitor clicks for that particular month. Now, by "visitor" it could mean users, or humans, that see interest in a particular Tablet PC and click on it for more information. It doesn't necessarily mean that it is the total market share for that particular Tablet PC, it is the overall visitor interest of that Tablet PC. "Visitor" can also mean search engine robots that are caching the pages for those Tablet PCs as well.
No, I do not believe that any of the manufacturers here fund the site to get an advantage in the Top 10 List. As I, and others stated, it is the general visitor interest of those Tablet PCs when they click on any Tablet PC link in the
Tablet PC Database. Not market share, or total percentage of owners who own that particular Tablet PC. Tiffany, Brian, and all the other Administrators here most likely add in Tablet PCs periodically so the database and the list is kept up-to-date with the currently available and coming soon Tablet PCs.
EDIT:
Also, this needs to be in the Site Suggestions & Site Help forum, and not the Press Releases & Announcements forum; this topic will be moved shortly.