Man-pages evolve also, and while each release of each distribution can be expected to have newer man-pages, nothing says that they will have the latest ones.
You have Ubuntu 14.04, which means "released April 2014". The manpage at man7.org is dated 2015-12-28 (part of release 4.07 of the Linux man-pages project), so it is not surprising you don't have it since your Ubuntu was released 18 months earlier. You do get updates, but those are mostly for bugs, not for improved documentation.
I am using Ubuntu 15.10, and I have a manpage dated 2013-07-30 (release 3.74 of the Linux man-pages project). That is earlier than the release of your Ubuntu 14.04, so one might think it should have been in your release, but I think you'll either have to trust the release engineers to provide you with consistent information, or use a distribution that tries to be as cutting-edge up-to-date as possible (I would investigate Debian sid, gentoo, arch).
Ubuntu 16.04 is out, so that would probably be a good idea!