You mean for everything someone intends to install using apt-get they should in fact assume that the PPA repo is 3 years old and google for the updated version? Isn't that rather counter-intuitive ?
This isn't the Bitcoin development teams fault. This is canonicals as they manage the repository. OP is installing from the main repository and not the third-party managed PPA which has a newer version.
Different distro's have different processes when it comes to updating packages in repositories but most have extensive an testing process before including it, which is why the Ubuntu version is outdated - they haven't got around to testing the newer versions yet. Most of the packages in the Ubuntu repository are outdated
intentionally. New features in newer versions may have bugs so they wait a while for it to mature before including it and normally only update when its necessary (security vulnerability is found etc).