The link below is to a New York Times article, which basically says that more people are completing marathons now thanks to training programs that require 3+ days of running a week. Some even incorporate walking. As long as the "long run" (20-26 miles) is done, most people will be just fine. They cited some major races having a 99% finish rate. This is obviously not how things used to be. Only the "elite" chose to run marathons, those who ran 6-7 days or 50+ miles per week. The fact that I finished one shows that things are definitely different now. Bottom line: these lower-mileage programs work.
I must agree with the warning that even with these relatively easier programs, it is not easy to go from, "Hey, I want to conquer this before I die" to crossing that finish line (and doing it again). Even doing 3-4 runs a week is tough after a while, especially if you don't live in a good running area and have a full-time job. Unlike half-marathons, you can't expect to go into a marathon with little training. It's a commitment that will save you from pain and/or humiliation. And you have to be in some reasonable shape before you begin, lest you'll injure/burn out and never want to run again.
I was not perfectly following the 18-week program (read: 4.5 months) I was on, but I think I had about an 80% compliance rate because my body and life got in the way. I did not expect to have to walk during the race because I hardly walked during training, but still, I didn't have pain after the race. Granted, I have some background in running, but I am rather baseline lethargic, as proven by the drastic drop in mileage lately on my part. Thanks, training program.