XML: Just enough standardization

Markup structure Whatever you do with XML, it provides a foundation set of rules. The rules are fairly abstract and extremely flexible, but the rules are strong enough that developers can create tools with XML, rather than specific dialects of XML, in mind.
Internationalization (i18n) XML's use of Unicode means that developers finally have an opportunity to break through the character set issues that compounded difficulties with moving documents among different environments. It doesn't magically let everyone speak multiple languages, but it does make it easier to deal with what has been a traditionally difficult problem.
Tools for establishing communication XML includes rules for describing the types of documents you are sending. They're in some transition, moving from DTDs to some flavor of schema, but these can build on the structures and labels of XML documents.
Existing infrastructure XML makes it easy to use the existing and relatively standard Web infrastructure.