As FeedStats comes along in a compressed file with subfolders, this plugin is actually stored under /wp-content/plugins/feedstats-de/feedstats-de/ which makes it invisible for WordPress.
It should just be stored under
/wp-content/plugins/feedstats-de/
right?
http://wordpress.org/extend/plugins/feedstats-de/
Yes, that plugin is broken. He's got one too many subfolders, the plugin PHP should be moved into the root.
When using the SVN you don't need to make your own subfolders if you don't actually need them. The main plugin PHP file must be down in the root of /trunk. The packager automatically creates the root subfolder on all the files.