The entire point to the site is that programming challenges using STDIN/OUT is not how you write code. So yes, you can cheat - but who cares. At least you get to write real code. Not to mention the number of things that can be tested for since you are able to use real testing frameworks.
STDOUT/IN based challenges cause developers to have to program esoteric challenges that they would never see in real life, and write code that they would never use for anything other than a challenge site.
STDOUT/IN based challenges cause developers to have to program esoteric challenges that they would never see in real life, and write code that they would never use for anything other than a challenge site.