There is no one format that is readable on all devices. And no one program will run on all platforms (not everything runs Java). The closest existing thing to what you propose is the Amazon/Kindle environment. Readable on Kindles, Kindle apps on pc, iPad, iPhone, Android devices, etc. However, if someone has a Sony or Nook, and the books have DRM, they would not be readable.
If you are serious, how would your idea be any different than any of the existing stores and/or apps?