Well, it should not be hard to imagine a program where order matters, or not? In my case it's natural language processing, where every word has several meanings and some of them are more probable than others. And I definitely want to try them first, even after some filtering and intermediate processing. It happens so that this processing is quite complex and involves many collection transformations. And having to write 'as LinkedHashSet' or 'as List' at least once in every such transformation doesn't quite encourage me :)

As I said, I don't see how defaulting to LinkedHashSet and LinkedHashMap could break anything. And it would make at least me much happier with Groovy :)