Ubuntu is a distribution based on Debian. By being a distro (distribution), it stands as a re-packaged version of the linux-kernel with lots of stuff on top (such as gnome). Since Ubuntu is branched from the last stable version of Debian, most of the core-utils that you want are actually same as those used in Debian.
I took a look at ubuntu packages and a search for
libc reveals the versions used in each ubuntu version.
The core of ubuntu is the Linux Kernel, and the Ubuntu Policy on keeping releases stable is available here.
When you develop for ubuntu, you can link your package against any version of the standard libraries using the deb packaging system that Ubuntu inherits from Debian. This allows you to specify a minimum version of the library that your package needs, for instance. You do not have to worry about compatibility issues across releases, rather check for the last version of the library that supported the features you are using. The Debian Developer Reference goes on details about this.