After downloading the R sources you should also download the recommended packages by entering the R source tree and running
tools/rsync-recommendedfrom a shell command line.
The above archives are created automatically from the Subversion tree, hence might not even compile on your platform and can contain any number of bugs. They will probably work, but maybe not. Use them to verify whether a bug you're tracking has been fixed or a new feature you always wanted has already been implemented.
CRAN itself does no longer mirror source snapshots (as of 2001-11-14), because it makes only limited sense to propagate archives that change on a daily basis through a network of mirror sites. When a snapshot reaches one of the final nodes in the mirroring process, there are already 2 newer versions available at the orginal sites.