Here's the link for the version comparison chart. http://www.sitefinity.com/purchase/license-comparison.aspx
In the left column, you'll see "content items" and next to it a small question mark, click on that and you'll get a pop up with your answer, which is that images count towards a "content item". That said, if they had 10,000 images in an /images/ folder off the root and not stored in the system I'm pretty sure that Sitefinity doesn't track these. The issue there of course is that there's no easy way to then access images in the file system as the "insert image" button in the editor doesn't support file system images (i'm now thinking this was their real reason for dropping this feature, if they can't control # of images they can't charge more $) and you also can't work with image albums etc in the backend. So if you were to store images in the file system your users would have to know html and how to manually insert image markup that pointed to the images folder (or you could write some custom code...).
Hope that helps.