Yes, but the namespace is present in the instruction tree (the XSL
document), so it is copied to the output - who knows in what weird way
the (XML) output might need the namespaces to be present? Imagine the
output is something like:

  <Constraint type="xs:decimal"/>
  <Constraint>xs:decimal</Constraint>

The QName may not appear in markup, but it appears in element or
attribute content; so it is okay for the XML parser if there is no
namespace declaration - but it might not be okay for the application
processing that document.

Alain Couthures
http://www.agencexml.com/xsltforms