This has been in the boto library for years, across multiple services. I noticed it when first using SimpleDB, switching it on in a production environment was much more expensive than we had originally calculated. I noticed the bizarre "Domain Validate" calls after pouring through logs of all boto activity.
I still don't agree with their reasoning to leave it default, once you try to do something on a non-existent domain/bucket it will throw an error anyway, and I would argue the "extra work" is much cheaper than leaving these defaults on which I would expect are completely redundant for most users.
The boto guys have justified it in the past: https://groups.google.com/forum/#!topic/boto-users/1DVfbo4CD...
I still don't agree with their reasoning to leave it default, once you try to do something on a non-existent domain/bucket it will throw an error anyway, and I would argue the "extra work" is much cheaper than leaving these defaults on which I would expect are completely redundant for most users.