To be fair to Wolff, it's not uncommon for deb and rpm packages of complex daemons (e.g. postgres) to include shell scripts - postinst, preinst, etc - that makes changes to the system, and which do have to be coded in such a way to handle re-execution after partial failure. Taking my /var/cache/apt/ directory as a (poor) sample, about 1/3 of packages had such scripts.