I'm printing out the article to read later, so I'm posting this based on a quick skim and comments that have been made here.
It does seem to me, though, that there is a sense in which prophecy has succeeded for the JW's. It has gotten them lots of new members and kept the existing members in a constant frenzy of works. As long as the members are convinced that Armageddon is right around the corner, they keep on slaving away and tend not to question things. When it starts to look like Armageddon might be a long way off, many start to scratch their heads and ask themselves why they are doing all this work, anyway? The prime example of the latter is the late 1970s, when the 1975 prediction had gone down the tubes and the numbers of publishers actually started to decrease for a few years.
That said, I'm not sure how anyone can make a credible defense of the Watchtower's prophetic record, in light of their 100% failure rate and their frequent claims to prophetic status, as well as the mandatory acceptance of each prophecy as it is issued under the threat of disfellowshipping.