Your perspective on self replicating nano bots as well as some other comments I have read here paint a picture of immense change in a short time once the technology is released into the wild. This view seems to ignore the fact that the capability to reproduce and to adapt are not the only factors. Any green and grey goo has to cope with the limitations of it's surroundings. Here are some examples: * available energy sources (food, sunlight, wind, geothermal engery, ...) * the rate of energy conversion into the energy source consumed (electricity or sugar/fats, etc). * processing power (along with it's energy efficiency) * energy consumption/efficiency when interacting with the environment * speed of reproduction * speed of adaptability (through intelligence or evolutionary techniques).

I don't wish to downplay risks involved but even if someone creates an intelligence that can outsmart them or a replicating system which they fear may over replicate the creator should be in control of enough of the environmental factors to keep it under control long enough to reduce their creations access to energy, resources. The real risk (from a perspective of self preservation) is not limiting their creation enough or overlooking sources of energy, information or whatever needs to be limited for this system.