I just downloaded a book I purchased via community pricing (The American Revolution). Since it is in the public domain I expected to be able to download it to Kindle but that option does not appear. Why not?
I am not sure of the status of this project, but when the feature was originally released in beta there were only a handful of resources available with this feature. That quickly increased. It may be they have just not gotten to that particular resource yet.
It also depends on the size of the resource.
Yes and Yes. If the file is too large, you won't be able to "send to kindle." It is also possible that the "send to kindle" resource just hasn't been created yet... Logos will have to comment further.