The point still stands that you were confusing symmetric and asymmetric keys. The largest RSA symmetric key that has been cracked is 64 bits, and that took ten years of an organized distributed process. Even taking Moore's law into account, 128bit keys will be secure for about 100 years. Only an unexpected breakthrough (such as quantum computing or discovered serious flaw in the algorithm) would speed that up.
My computer uses 3w in standby. That corresponds to 2kWh/month. Which costs about 40cents. It's not worth that much effort to save 40cents/month.
Overall, I average 400w at home (~300kWh/month). Using a zero-watt standby computer would reduce my power consumption by less than 1%. That is not very significant.
I can see how this might help for business that have lots of computer, but in most cases, those companies don't even put their computers in standby when not in use currently, so a zero-watt standby mode won't help them either.
There are much better ways of saving power, like encouraging companies to put desktops in standby when not is use for any length of time. That would save much more than 3w per computer.