It's also that it's extensible (primarily because of namespaces) - you can mix and match schemas so long as one of them uses xs:any. This brings up another way

It's also that it's extensible (primarily because of namespaces) - you can mix and match schemas so long as one of them uses xs:any. This brings up another way to avoid being called a bozo: namespace your XML. You're throwing a major advantage away if you don't, and if you don't need/understand that advantage then you're better off using a different serialization format.