To be more specific, see this ML post: http://linux.derkeiler.com/Mailing-Lists/SuSE/2003-11/2640.html

The old SLES had all the bzip2 files ( libs and includes ) in a whole monolithic package bundled with the system.

The SLES 11 version splitted the packages in a bzip2 package for the libs and a bzip2-devel one for the includes.