"No OS should ever require 3rd party programs in order for it to become useable."
You must be very easily pleased.
I've replaced the built-in windows copy routine, because it's a little bit buggy, and doesn't offer features I need.
I've replaced the delete routines - strictly not needed, but the extra reporting is nice.
I've replaced windows explorer, because, well, it doesn't come close the to productivity levels I have now.
I've replaced the built-in browser, because it was Internet Exploror, do I need any more reason than that?
I've replaced the "built-in" email client - which they force you to download - because mine is better.
I've replaced Media Player. Because I can.
I've installed my own security manager. Not that hard to get better than BitLocker.
I've replaced my command prompt. Batch scripts feature heavily here, and beating DOS isn't hard.
I've replaced the bulit-in CD/DVD burner. Mainly because I want to get work done the way *I* want to.
-- And that's just replacing the built-in utilities - wanna get me started on actual add-on productivity software?