Isn't this guy reinventing a simplified wheel? We already have tools like Capistrano and Fabric or Rex (which does quite a bit more than just application deployments).
Thats like saying why understand how writing a file to disk works when we have things like notepad and emacs. What do you think these tools do under the hood?
After my experience of Capistrano and Fabric, I think it's a wheel that needs to be reinvented. Capistrano: hardcodes way too many things, underdocumented. Fabric: reimplements ssh (poorly). Moving from Capistrano to a custom script I ended up with less code and higher maintainability.
