I would argue that XSDs and namespacing are pretty much a necessity when you're trying to represent structured data. I agree that DTD and especially XSLT can be

I would argue that XSDs and namespacing are pretty much a necessity when you're trying to represent structured data. I agree that DTD and especially XSLT can be painful, but they're certainly more optional. Being able to generate XSD from your code and then just pass that off to someone else while remaining generally language-agnostic is extremely powerful. JSON is cheap and easy, but it's really not that great.