The Wikipedia entry on Friedman Units tracks over 30 different cases between 2003 and 2007 in which someone labeled the "next six months" as the "critical period in Iraq". Apparently one of the worst offenders is journalist Thomas Friedman after whom the unit was named (8 different predictions in 4 years). In similar news, some of my colleagues in Artificial Intelligence (you know who you are) have been predicting the spectacular success of their projects in "3-5 years" for as long as I've known them, that is, since at least 2000.
Why do futurists make the same mistaken predictions over and over? The same reason politicians abandon campaign promises and switch principles as expediency demands. Predictions, like promises, are sold today and consumed today. They produce a few chewy bites of delicious optimism or delicious horror, and then they're gone. If the tastiest prediction is allegedly about a time interval "3-5 years in the future" (for AI projects) or "6 months in the future" (for Iraq), then futurists will produce tasty predictions of that kind. They have no reason to change the formulation any more than Hershey has to change the composition of its chocolate bars. People won't remember the prediction in 6 months or 3-5 years, any more than chocolate sits around in your stomach for a year and keeps you full.
The futurists probably aren't even doing it deliberately; they themselves have long since digested their own predictions. Can you remember what you had for breakfast on April 9th, 2006? I bet you can't, and I bet you also can't remember what you predicted for "one year from now".