Apparently the difference in tax situation between BookBaby (not requiring a U.S. tax number) and Amazon (etc. that do), is not necessarily inconsistent with the way tax is handled in the U.S.. I won't try to pass on my accountant's explanation, I'm not certain I understood all of it, but the end result is that he was not concerned about the difference.
ETA: This is not formal advice, just passing on what I was told. The upshot being that I am no longer concerned about what I had thought was an inconsistency.
Last edited by gmw; 11-04-2012 at 08:41 PM.