What changes with XML

a.k.a. "No pain, no gain"

XML is not a silver bullet!
XML is like a "super-ascii", it is a low-level standard.
XML defines a syntax, but no semantics: applications have to define the semantics of the data. In particular displaying XML data is not as simple as displaying HTML
a lot of people find it hard to shift from "creating a document that looks good" to "creating properly identified data"
While the XML recommendation is simple, it comes with a host of related-recommendation which are not.