Personally, I would have speculated (again) that these machines have such a short lifespan (due the seemingly ever exponentially increasing hash rate) that you would want to continue to run them while they are still profitable and with the passage of time they are going to become, more or less giant paper weights.. or maybe ONLY heaters b/c they are otherwise running at a loss.
My first-gen BFL ASICs were obsolete last winter. By the end of winter even underclocking them wouldn't have helped.
Indeed I see my miner as only a heater. Even if I only earn a few satoshis, I still feel as if I'm contributing to the network.