I'm only giving my opinion from the point of view of a consumer with no tech experience....
The first thing that struck me, when I saw the logo, was the large "O". I immediately associated it with "open". That may be because I am a member of MR and am familiar with DRM and DRM free formats.
Your comments about not adding ePub on the book make sense. A consumer would only have to learn what a symbol represents to quickly recognize and identify it on other sites (like learning what the adobe pdf symbol means).
I also like that the symbol would be clear either in color or B and W plus recognizable in various sizes.
That's my little ole 2 cents worth..