Devin Smith says "I don't think it belongs in the copyright notice for anything (software, electronic documentation, etc.) that is being licensed.
It belongs in books that are sold where, in fact, all rights (e.g., to reproduce the book, etc.) are being reserved in the publisher or author.
As Boost grew, it became unmanageable for each Boost file to have its own license.
Users complained that each license needed to be reviewed, and that reviews were difficult or impossible if Boost libraries contained many different licenses.
I would expect that, unless we're remarkably brilliant (or lucky) in drafting the standard Boost license, the standard license won't satisfy the legal departments of all corporations.
I imagine that some will, for instance, absolutely insist that licensors provide a warranty of title and provide indemnification for third-party intellectual property infringement claims. (If I were advising the corporations, I would point out that they're not paying anything for the code and getting such warranties from individual programmers, who probably do not have deep pockets, is not that valuable anyway, but other lawyers may disagree.) But this can be addressed, not by trying to craft the perfect standard license, but by informing the corporations that they can, if they don't like the standard license, approach the authors to negotiate a different, perhaps even paid, license.
One other benefit of adopting a standard license is to help ensure that the license accomplishes, from a legal perspective, what the authors intend.
A different implementation is free to use the same logical interface, however.
Interface issues have been fought out in court several times; ask a lawyer for details.