That is a very narrow view of XML. AJAX works by exchanging XML fragments with the server app. JSON may replace XML here.

Flex in addition uses XML to describe the UI itself (like XAML and XUL). XML is not just about user interface. It is also used for data exchange, object communication (webservices), creating several industry specific vocabularies (fixml, acord).

For simple data exchanges between a web client and its server within the same application it's probably more practical to use JSON or Flex, but before writing XML's obituary let's not forget that it provides the syntax for web services (the basis of SOA) as well as a myriad markup languages, some of which have by now solidified as industry standards. I personally think that XML is by far the best that ever happened to enterprise data exchange, which for decades had been hindered by mutually incompatible custom EDI formats. This doesn't mean that XML is immortal, but given its traction it will probably stay around for a while and the problems associated with payload verbosity will be resolved sooner or later by better compression algorithms, possibly at the network hardware level, making it transparent to enterprise users.

Trackback Added: Is XML past its prime?; In Today's World of AJAX and Flex, Is XML Past Its Prime?
? Does XML need to be regarded as a good idea whose time has come and gone? There are plenty of capable replacements availabe when using AJAX and Flex. Some examples that come to mind are J