Most mined coins never hit the open market. Many miners are only recouping equipment and electricity costs and holding the rest.
This is not an explanation; bitcoins are fungible. Everything except transaction volume would look identical if all the miners sold off every coin they made and instead a different group bought up all those coins; you need to explain why there are so many people willing to hold bitcoins. Whether those people going long on Bitcoin happen to have mining rigs or not is irrelevant.
Looks like a deflationary spiral
The bitcoins that I had set aside for a Cryonics contest two years ago (and were unredeemed) are suddenly worth a lot more.
Details: I had added 10 bitcoins to get things started, and there were 4.75 worth of additional donations. These were partially lost when the hosted online wallet that I was using (MyBitcoin) was hacked, but 49% was recovered. As of today, after refunding part of the donated money, it is now worth 5.2675. I will be adding from my personal store to bring it up to an even 5.5. At $140 per coin, the new total is $770.
I've decided to follow the buy-and-hold strategy for at least another year, since it worked so well. I don't have exact details on what I'll do with it, but it will not be converted or spent for at least one year, and will eventually be used for promoting cryonics in some way.
Some things I have in mind if it gets big include:
Contributions can be made to:
1Jdn36JUwvJdr3Qiie4aAseFdcoTsND9Qo
(Updated, since the previous address was attached to my personal wallet on an outdated client, which was causing money to be moved out of it by accident. The above is a brainwallet with a reasonably secure passphrase, generated using Blockchain.info.)