2. Section 3.2 of 3688 describes what gets registered when registering an XML namespace. It says "XML Namespaces ... are named by a URI. They have no real, machine-parsable representation". Yet the template includes a chunk of XML to be registered. It's not needed, so why is it included? All that needs to be registered is the urn:ietf:params:xml:ns:simple-filter URN.
That's how I've seen it done. Check out
http://www.ietf.org/rfc/rfc3858.txt and http://www.ietf.org/internet-drafts/draft-ietf-simple-iscomposing -03.txt (in author's 48 hours)
I'm aware of other instances like the ones you've pointed out. Frankly, though, I think they're wrong. There's nothing in 3688 that talks about registering any XML as part of registering an XML namespace. It's not needed, so it should be removed. -Scott-