Even if some one doesn't have a broad band connection they can still have a stable release installed on their system. Just tell me having a separate repository for every release, doesn't it increase the burden on package maintainer, updating and patching the packages.
Having just on repository reduces the burden. Arch linux has just three main repositories for all their releases:
1)Core:It contains Arch core packages and some additional software.
2)Extra:It contains all Arch packages that didn't make it into core.
3)Community:It contains packages from the AUR that have enough votes and were adopted by a TU.
Check out this link to get a better idea http://wiki.archlinux.org/index.php/Official_Repositories