I don't fully understand, the official Google Reader logo looks exactly like the "unofficial" logo, so did Google copy the "unofficial" logo or was it a copy of Google's? This isn't addressed in the blog post.
I'm not a lawyer, but the author's image is in fact a derivative work of the original, and as such I'm not sure there's much he can do in this case. If it were an entirely unique creation that was being used without permission you'd have more options.
http://googlereader.blogspot.com/2009/05/google-reader-on-yo...
http://bonte-pierre.blogspot.com/2008/02/google-reader-for-m...
Do a Google Image Search for "google reader" and use the Search Tools button to restrict the date to before June 2008.