I've heard people say that, for example, the fact that a Linux system is made of pieces from a million different projects is beneficial to its evolution because

I've heard people say that, for example, the fact that a Linux system is made of pieces from a million different projects is beneficial to its evolution because doing this kind of crap simply isn't an option. Solid, well-defined interfaces between components are a must (and if they aren't an absolute must, they won't exist - not necessarily because of laziness but because of deadlines) in systems that are made from lots of independent groups' components.