I agree with this advantage, that's what I meant with "the modularity aspect"; a non-OO programming language with support for modules also offers this. However, as soon as you get to non-trivial and often gratuitous inheritance hierarchies, it gets in the way of at least readability and probably also maintainability. Example: instead of String, you get AbstractMutableStringOfWesternCharacters, all the way to ArrayBasedStringOfASCII and everything in between. Suddenly to understand one function, you have to read and understand n classes, because they are part of the inheritance chain.