Due to high maintenance cost of scripts related to the Arch Build System, we have decided to deprecate the abs tool and thus rsync as a way of obtaining PKGBUILDs.
The asp tool, available in [extra], provides similar functionality to abs. asp export pkgname can be used as direct alternative; more information about its usage can be found in the documentation. Additionally Subversion sparse checkouts, as described here, can be used to achieve a similar effect. For fetching all PKGBUILDs, the best way is cloning the svntogit mirrors.
While the extra/abs package has been already dropped, the rsync endpoint (rsync://rsync.archlinux.org/abs) will be disabled by the end of the month.