Development of Creative Commons licenses

[wiki_tomos <wiki_tomos AT inter7.jp>]

Hi. I am not a lawyer, and I do not recall any particular source to cite, 
but I had the same question before, and below is how I interpret the 
license. In short, the absense of the "-sa" element does not mean that 
the MiddlemanGuy can offer the whole of derivative work under any license 
term, 
but it means that the copyrights in the original work are still available 
only under the CC-by license. And the MiddlemanGuy cannot do anything with 
it. 

In a word, the answer is no. 

Here is a more detailed interpretation: 

The creative expression created by the MiddlemanGuy is, well, his own. 
If he wants to license without an attribution requirement, fine. The 
MiddlemanGuy is not obligated to offer his work under CC-by or anything, 
because the OriginalAuthor did not use -sa license. 

However, the CC-by license (at least the versions that I know) does not 
offer the MiddlemanGuy to sublicense any of other parts. That is, he 
cannot give permission or impose condition regarding Client's use of the 
creative expression MiddlemanGuy did not create. That can be done only 
by the OriginalArtist. 

The copyrights regarding the creative expression created by the 
OriginalArtist is still completely OriginalArtist's. And a 
CC-by license has a provision that any recipient of the work, 
or its derivative receives the same CC license regarding 
the original work. That means that the Client, when he receives a derivative 
work (or Adoptation, in CC-by-3.0's terminology), he is offered the CC-by 
license by the OriginalAuthor regarding the original work. 
This provision is under the Miscellaneous section of the license. 

That means, the MiddlemanGuy cannot release the Client from the 
CC-by's restriction that he needs to attribute the OriginalAuthor. 
The MiddlemanGuy does not have any right to do that. 

If you look at the -by-sa license, in contrast, the Miscellaneous section 
does not have the provision I am talking about. 

I suppose MiddlemanGuy might want to impose a term or two, to prohibit 
Client from starting a competing business using what Client bought from 
the MiddlemanGuy. That's fine. Because OriginalAuthor did not restrict 
how MiddlemanGuy can license his copyrights in the derivative work, 
he can impose such a term. But again, the Client is free to use 
the OriginalAuthor's creative expression without being restrained by 
such a term. 

Best, 

Tomos