When the hashing power has decreased and rigs were sold. But yeah people are in denial, that's what gives scam artists alternate cryptocurrencies a free hand.
Deepbit disagrees with you. Over the past month the hash rate there (measured, not estimated) has gone from 5 terahash to 5.5 terahash. It was going up 50 gigahash a day as the price went below $10, and has since flatlined -- but it has not decreased in any measurable way.
*MY* remaining mining hardware is on craigslist, I don't deny it. Already sold two 5830s for $120 each, hoping for a difficulty drop or price pop to sell the last 2. But that won't be the general case until FPGA and ASIC miners make video cards as obsolete as CPUs.