On 15 Sep 2015, at 15:51, Filip Konvička
I think removing the copyright notice would not deprive anyone of their rights, and probably is an allowed modification under the Boost Software License (whereas removing the BSL notice is not).
And it looks like I'm wrong here - the BSL explicitly requires the copyright notices to be retained (as Jonathan correctly pointed out).
I think this is pretty much it.
The copyright holder is the one that (can) release the source under various licenses, in this case the boost license. Without a copyright statement you would not know who released the code under the boost license, and it that case the boost license might be invalid. That's the reason that the boost license requires a copyright statement, so that people can find the copyright holder and check if he indeed released the code under the boost license.