Yes, this is a great topic, and one that deserves serious thought and discussion.
When Marcus Borg visited our church several years ago, I recall him saying about someone who claims not to believe in God, "Describe for me the God that you think you don't believe in." Then, a response. And then "Well, I don't believe in that God either." Borg made a telling point. And of course he DID believe in God, as does Jack Spong.
Being curious about these questions, I just looked up on the web the "definition" of God. Here is what the Oxford dictionary says:
GOD: NOUN1(in Christianity and other monotheistic religions) the creator and ruler of the universe and source of all moral authority; the supreme being.
2(in certain other religions) a superhuman being or spirit worshipped as having power over nature or human fortunes; a deity
When Spong says he is a non-theist, he is saying that he does not believe in God as defined just above. He and many other writers in Progressive Christianity have chosen the term "non-theistic" to convey that they don't subscribe to the above understandings of God: They do not understand God as a "Being". But we can be absolutely certain that Bishop Spong does believe in God, as do many other progressives who have written in this area.
So, rjunker, I believe you are quite right from a logical perspective and a traditional understanding of the meaning of God. But for me, the definitions in the Oxford dictionary are too limiting and they miss the mark of what we may mean by the term "God" in the 21st century. As I've read Jack Spong's columns and books, I've gained an appreciation for his more expansive understanding of "God" -- one that quite a few religious thinkers of our time seem to embrace.