It's because both the thumbnail images and the binary geometry are in the "resource fork" of a Mac file, a part of the mac file system that has no equivalent on Windows. When Poser got ported to Windows, they dealt with all resource forks by just making them .rsr files, regardless of the resource type. On the mac there is still an obvious distinction between the two: the thumbnails are 'PICT' resources and the Geometry files are 'ACTR' resources. -Adam