URIs as namespaces

Something which has always seemed obvious to me is that it should be
intrinsically obvious on the "client side" whether a name refers to
something which can be explicitly retrieved or whether it rather refers
to something imaginary that has no internal representation in a
computer. This becomes obvious in a variety of contexts:

 * students in any XML class ask about whether you must be connected to
the Internet when you use namespaces -- no matter how many times you
tell them no, they do not believe you because it is so non-intuitive.

 * email clients automatically "highlight" namespaces because they have
the same syntax as URL-retrievable information

 * XML language lawyers have huge flamewars about what XML vocabulary
should be the "referent" of the namespace link (XML Schema? DTD? Some
meta-schema document? Stylesheet?)

 * If there is such a referent, then it becomes ambiguous whether RDF
properties, etc. apply to the retrievable referent or to the abstract
"namespace."

I see the benefit in treating retrievable and irretrievable resources
"the same" in some contexts but I see no benefit in providing no
syntactic signal of whether they fall into the former or latter
category.

 Paul Prescod