It's not like the stuff inside the script can't be standalone classes of the "do one thing and do it well" variety --they just don't get to be processes.
On the other hand, you may not want to reimplement sed, grep, etc in your scripting language of choice. There are times where a good "perl -e" can be very useful in a shell script.
It's not like the stuff inside the script can't be standalone classes of the "do one thing and do it well" variety --they just don't get to be processes.