XHTML 1.0 DTD and namespace declaration

The XHTML 1.0 DTD contains this namespace declarations:

<!ELEMENT html (head, body)>
<!ATTLIST html
%i18n;
xmlns       %URI;          #FIXED 'http://www.w3.org/1999/xhtml'
>

However, this conflicts with the the following paragraph in section 4
of the Namespace recommendation:

This constraint may lead to operational difficulties in the case where
the namespace declaration attribute is provided, not directly in the
XML document entity, but via a default attribute declared in an
external entity. Such declarations may not be read by software which is
based on a non-validating XML processor. Many XML applications,
presumably including namespace-sensitive ones, fail to require
validating processors. For correct operation with such applications,
namespace declarations must be provided either directly or via default
attributes declared in the internal subset of the DTD.

Best Regards
Mikael