For the millionth time in these forums. The price of BTC has absolutely nothing to do with the price of mining. The difficulty will adjust towards making mining a break-even venture. The difficulty rate lags the price due to the time it takes to bring miners on and offline. The price is solely determined by supply and demand.
Not all bitcoin users are speculators, there are many bitcoin supporters, they don't care too much about the exchange price of bitcoin, they just want to get more coin. They can either mine or buy the coins. whichever is cheaper
At $200+, even the GPU mining do not need to care about the electricity, so these people will just buy more GPU to mine the coin, the number of these people are huge, so if they don't buy coins, the exchange rate will lose support of these people
When the exchange price has falled below the normal GPU miners's electricity cost, they might still mine at a loss, but there is always an exchange risk that price will never recover for a long time, and they have to pay the electricity, so many of them will stop the rig and buy the coins directly, and that will support the exchange price
Of course when the coin is in a fast adoption phase, the demand could drive price up, but I suppose most of the people who are really interested in bitcoin have both computer and economy knowledge, so mining or buying will always be their consideration, and works as a rough guideline for the base price of bitcoin