Deflation is just one form of asset appreciation. If this line of reasoning were true then we would never see anyone selling anything that appreciates in value. But this is a very one-sided way to consider this scenario--it only takes into account the supply side. When the asset is appreciating, the demand side takes this into account as well and is willing to discount their asking price to take this into account. You saw this play out with real estate several years ago, and with gold more recently. It may blow out the bid/ask spread a bit, but eventually there will be people who need to sell their asset to buy something else, or there will be people who want the asset badly enough to pay what people are asking.
I think this argument can be discounted simply by looking at the current state of things--people are still spending bitcoins even though the recent appreciation dwarfs any built-in deflation. Sellers may need to discount their price to get people to pay in bitcoins, but even that doesn't seem to be happening yet.
One problem here is that you're considering the currency as an asset that should appreciate. The argument of most economists today is that currency should not appreciate because it encourages hoarding what is essentially a useless non-good, it's just a token for convenience of value transfer. If real goods appreciate, it's because the value offered by that good to the marketplace has increased, so the market pays a commensurately larger price. If currency appreciates on its own, people will want to hoard it, and will only spend it on things they deem highly valuable. Perhaps you can argue that this is better in the long run and would stop rampant consumerism, but it's pretty obvious that without rampant consumerism, many people would be making less money.
People aren't really spending bitcoins in a meaningful way. They're using it as a passthrough for the dollar, basically. I have a Bioshock Infinite key that I want to sell. Will let it go for 1.5 btc. Why won't this offer be taken up now, when just a couple of weeks ago it would've been considered a fair deal, and just a couple of months ago it would have been considered a GREAT deal?
You're just noting the difference between a centrally-managed currency and one that's not. The value of bitcoins tends to move quite a lot lately, so it's like trying to price something in AAPL stock or something right now--you have to peg the value to a slower-moving reference currency. (And that's typically how BTC-denominated goods are priced, for example on the Silk Road the product prices are pegged to the USD.)
But that's not to say that centrally-managed currencies don't fluctuate either, because they do--just, typically, in the other direction. If I tried to find a gas station that would sell me a gallon of gas for $2USD today I'd be out of luck, but 2-3 years ago I'd be able to go anywhere in America and get that deal.
>If I tried to find a gas station that would sell me a gallon of gas for $2USD today I'd be out of luck, but 2-3 years ago I'd be able to go anywhere in America and get that deal.
That illustrates that the price of oil fluctuates. The USD hasn't dropped in value by 50% in the last two years.
Most of currency is fluctuation is fluctuation relative to other currencies. If the price of the Icelandic krona plummets relative to USD and GBP, it doesn't mean that all the prices in Iceland immediately rise to compensate. People in Iceland are still paid in krona and buy things in krona for approximately the same number of krona.
But if the price of BTC rises suddenly, prices do suddenly decrease because at the moment it's just a proxy. There's no real internal market: there aren't people who are paid in BTC and have their savings account in BTC and make their mortgage payments in BTC and buy their food in BTC.
So BTC really isn't like other currencies. It's fluctuating massively even from an internal market perspective.
I think this argument can be discounted simply by looking at the current state of things--people are still spending bitcoins even though the recent appreciation dwarfs any built-in deflation. Sellers may need to discount their price to get people to pay in bitcoins, but even that doesn't seem to be happening yet.