Microsoft Team RSS Blog: We’ve adopted the following overriding principle for IE 7 and RSS platform in Windows Vista: We will only support feeds that are well-formed XML.
http://blogs.msdn.com/rssteam/archive/2005/11/03/489065.aspx
Luke Hutteman: Maybe there's an exception to Postel's law after all.
Randy: This shows great community leadership on Microsoft's part. It also means that some Windows-based RSS readers will refuse to use the RSS platform in Vista and claim their RSS aggregator accepts more feeds. When that happens I'm gonna be ready to pounce.