This is a really interesting point, I'd also be interested in finding out what makes most businesses and most blogs fail. From my limited reading, I think it's likely that the idea of both is overly hyped-up, but once the harsh reality sets in about how difficult a business or continuing to blog are, people will quickly abandon ship, thus the start-and-run behavior.
The barrier to entry is also lower than ever. This means there is less incentive to truly think through every detail before starting a new endeavour, which leads to a higher percentage of failure. As has been discussed ad nauseam on HN, this is not necessarily a bad thing.