Real world software engineering - VIII

In Real World Software Engineering, one may create code keeping in mind that the stuff may have multiple uses in different scenarios. Instead of closing the door to infrequent scenarios, why not allowing the developer to include other basic functionality - perhaps even unsupported - so that customers can apply the software where it is useful? I get upset when I want to use software that has very strict functionality and it doesn't work for me (I'm usually trying something complex... that doesn't work until I 'bend' the software).