here is a snip from
http://www.microsoft.com/windowsserver2003/evaluation/overview/dotnet/runningondotnet.mspx
Content developers can use .NET technologies to create XML-based content
that is easily sharable between workgroups and Web sites. The Microsoft.com
Web content development team built the Windows Server 2003 product site,
using XML and XML Web services in order to showcase the .NET functionality
in Windows Server. You can identify XML-based pages on Microsoft.com by
their .mspx file extension, rather than the more common .htm, .html, or .asp
extensions used by other Microsoft.com pages. One benefit to XML-pages is
that XML templates and schemas are easier to work with when localizing Web
content for other languages. A single schema can be reused by several
international Web sites.