A simple reason why Bitcoin will never go to $0 is because there are people out there that will snap up every last single one at a given price point (myself included). Keep that in mind next time you are in fear of $0 Bitcoin.
Or would the chain change difficulty to accustomed the new mining computers?
But that'll take 2 weeks. Most other coins update difficulty every block. BitCoin takes 2 weeks right?
That's right - not a perfect system, but it has worked pretty well so far.