Seems when WSDL 1.0 (Sept. 2000) was first developed by IBM, Microsoft and Ariba, W3C was not involved, so these giant corporations happened to invent a namespace neutral to anyone of them. (neither "http://www.ibm.com/..." nor "...microsoft...") I guess.
And the namespace doesn't change to "www.w3.org/wsdl" until W3C has finally got the copyright of wsdl 2.0.
Maybe this explains.
subject: Why namespace for wsdl is not "http://www.w3.org/wsdl"?