A more accurate question would be how many bitcoins are in circulation. Because that is what really affects the price, isn't it?
That's a good point. Coins that are horded are like lost coins, in that they are unavailable for trade.
Like, but not the same. These can, and likely will, renter circulation given the right price.
Yes, but not really. Whether there be 21 million or 18 million really doesn't matter. What matters is that we know that bitcoins are rare, how many bitcoins are available for purchase and for how much those who own bitcoin are willing to sell them for. That is what affects the price when it comes down to it.
Nobody cares how many ounces of gold there are in the world..
I can't say I disagree that scarcity is the primary value proposition, but I'd say the dead Bitcoins do matter as they won't be turning up in a crash.
I believe the current "crash" has a lot to do with companies like Dell and Overstock accepting bitcoins. Having new opportunities to spend bitcoins would cause previous hoarders to spend. Dell and Overstock don't hold the coins, they cash them out for another quick sale, which puts more coins on the sale side than the buy side. In the future, as more people are regularly transacting in Bitcoin, this downward pressure should equalize. But for now, there aren't enough people buying bitcoins.