Some are holding coins in order to spend them later when it's easier and safer and they can buy the normal things they would buy in their everyday life without a second thought, and without having to change back to fiat... yes that doesn't account for the transactions now, but as merchants accept more and infrastructure develops, if the speculation does drive the price up, I am assuming people will want to spend their (now more valuable) coins... obviously this comment also doesn't have much to do with the transaction volume affecting the price on the exchanges now, but on that subject I will also put forward the idea that it may not have much impact on the exchanges, as day to day purchases of coins to spend coins would be inefficient, I will assume that many people already have large stashes of coins they might spend.... finally also bear in mind that some of the philosophy of bitcoin (for some people, and anecdotally a majority) is not to spend spend spend to drive a consumerist economy. As mentioned before, just because the economy is not full of high volume transactions, doesn't mean it's not living and breathing.
Stream of consciousness waffle here so take it or leave it
