This canon comes from his "Musical Offering" which are a set of pieces dedicated to Frederick the Great of Prussia (a flutist like me :-) ) all based on a single awkward theme given to him by the king, as a kind of challenge.
So I guess my point is when you look at this as one of a collection of many variations, renderings, and re-imaginings of a single short melody, with an eye to the importance that Bach placed on the aesthetic idea of an economy of material, that this becomes more than just a clever trick.
Although I agree Bach probably wrote it in less time than it took him to write it down. And I don't think he would have imagined people after his death would be playing it, let alone making CGI youtube videos and run-on sentences discussing it on internet message boards. :)