Hahah what a silly quote, damned if it isn't true though.
According to the Jargon File, jwz coined it "to express his belief that all truly useful programs experience pressure to evolve into toolkits and application platforms." From the little I know about Wolfram, it has been such a toolkit and platform for quite some time already. http://www.catb.org/jargon/html/Z/Zawinskis-Law.html