Your "XML" examples weren't even well-formed! That ought to lend no little credence to my claim that XML is not easy for humans to write.

What validates crontab, for example?

That would be crontab. If you were writing that program, you'd have to create code to process the arguments somehow anyway.

I agree that an XML processor can check the well-formedness of a document, but I have severe doubts that it can check the semantics of the entire document for anything but trivial configurations, where each option is completely independent and, likely, idempotent.