For all those people wondering about this... I recommend doing some of your own digging to understand what is going on. 90% of programs do leave files behind. Want to see them? After you deleted the app and emptied your trash open a terminal and run:
cd /
sudo du -ah | grep <program name>
Substitute the <program name> for a part of the name of the program you are deleting. All this is doing is listing all the files that match that string.
Example, if I delete a program called "bookclub", I'd probably run 'sudo du -ah | grep bookclub.
Most of the time you'll find a handful of very small files. Nothing to be concerned about.