Dave Orchard wrote, and Don Box concurred, that it’s a good thing to avoid registration at the likes of IANA and IETF. I also concur, as my hopefully-soon-to-be-BCP Internet Draft with Dan Connolly describes.
Where I disagree with Dave and Don, is summed up by Dave;
XML changes the landscape completely. Instead of having a small number of types that are registered through a centralized authority, authors can create arbitrary vocabularies and even application protocols through XML and Schema. In the same way a client has to be programmed for media types, a client must be programmed for xml types and wsdl operations.
IMO, XML doesn’t change the landscape in that way at all. It’s always been possible to have an explosion of data formats and protocols; 10 years ago you could have done it with ASCII and ONC or DCE. The fact of the matter is that we don’t see these things on a large scale on the Internet because most people don’t want them. Not only is it expensive to develop new ones – even with a fine framework for their development, such as SOAP & XML Schema – but you’re very typically left amortizing that expense over a very narrowly focused application, such as stock quotes or shoe ordering, or what-have-you. The Web and Semantic Web efforts are an attempt to build a supremely generic application around a single application protocol (HTTP) and a single data model (RDF). Now that’s landscape-changing.