Send your own messages

More the original XML message XML lets developers create whatever formats they want, for whatever transmission or storage they like. What exactly do the protocols add? An envelope?
Roll your own Sending XML isn't exactly rocket science. Socket connections, HTTP POSTs, or instant messaging are all perfectly fine modes of transmission over networks, and dropping files for another program to pick up later is yet another option that goes nowhere near a network.
Maximum flexibility Probably for cultural reasons, the notion of XML messaging doesn't seem to have developed as powerful a "thou shalt validate, yea, thou shalt centralize thy processing" model as other approaches. Building an XML listener that routs messages on assorted structural criteria isn't all that hard.
Lack of standardization has its costs Most businesses don't appear as interested in flexibility as in predictability. "Do your own thing" works very well for ad hoc communication, but tends to make CTOs shudder.