I agree with Stardust. Business wise it would only make sense to invest so much resources for a new generation product's line vs legacy products.
And as a second thought (which should have been my first one

) although OSX runs on old 9500-9600 machines... to my knowledget it's impossible to run OSX 10.4, so I guess definitely not OSX 10.5!
The good thing (as sad as it is) is that I now have the answer to my question.