I guess there are not so many people who are installing it via synaptics or similar. You can use a PPA for regular updates:
Examples:
https://launchpad.net/~rwky/+archive/redis
https://launchpad.net/~chris-lea/+archive/redis-server
You can also create a script that automatically downloads and compiles it for you or download and install it manually from the official web site.
Popular software gets more attention obviously so there are some packaged that are extremely old for the simple fact that not that many people download them OR the package maintainer just gave up. Some packages are just forgotten I guess and they don't even bother removing them.
PS: Just because something is not officially supported (even by the developer) doesn't necessarily mean that it is not used by some. There are plenty of examples out there. :)