I don't think that's true at all. If you use Ubuntu, broken packages are ultimately your responsibility unless you're paying for support from Canonical. In both Ubuntu and Arch Linux, changes will be handled carefully by the maintainers to try to avoid breakage where at all possible. The difference is basically that on Arch you're supposed to be able to handle basic sysadmin tasks yourself, which means that Arch Linux will ship breaking changes (with a mailing list warning) that require you to run a command or two yourself. Even with that qualifier, this is uncommon.