Nobody is selling over cost here.
How do you know? Is there evidence? Or is it just implausible that people who spend tens of thousands of dollars on mining rigs need to recoup at least some of their money to pay the bills? Lets be generous and say the cost of mining is half the value of the coins...that means collectively bitcoin miners are spending $25k
per day on electricity...that's $10M per year...that's a freaking lot of money to spend on electricity...why are you so sure that everyone doing this is so rich that dropping a few hundred thousand dollars in the short run is no big deal?
At first currently the price is irrelevant there is no volume at all right now.
I can't quite parse that sentence, but the price has been below $12 for over a month now. According to bitcoin charts, MtGOX has traded 1.2M BTC in that time. That's quite a lot of volume to say that prices are below $12.
Second, these are most likely old coins and these doesn't even have to be sold by miners.
Why is this 'most likely'. Do you have any evidence to support it? It could be, I don't know...I'm just wondering why everyone seems so sure it's
the explanation. Anyway, it doesn't actually follow that old coins don't have to be sold by miners. If you mined old coins and new coins and you need to pay some USD bills, why would you necessarily trade in your old coins rather than your new coins?