Postel's Law doesn't provide you with a clear culprit to be angry at:

> A plan for getting from A to B followed by (or composed with) a plan for getting from B to C is a plan for getting from A to C. Well a correct plan for getting from A to B when composed with a correct plan for getting from B to C, if each of the plans “is mostly right if the piece after is so nice to fix up a few mistakes” you really don’t know what you have. You may have nothing.

> Correct code remains correct under various compositions and transformations (that may happen in the future). Code that is working only due to pity often does not have this property.

http://www.win-vector.com/blog/2010/02/postels-law-not-sure-who-to-be-angry-with/