Nobody has even come close to explaining why they think that the reward change will affect the value of BTC.
I think it will have no (short term) effect whatsoever. There are 10 million BTC, 25 less every 10 minutes is nothing. The demand for bitcoins won't change because of the lower reward. The number of miners will drop by half along with the difficulty, but the number of bitcoins produced will still be 25 every 10 minutes.
So, tell me, why will the price change as a result of the reward being halved?
Okay simple economics:
A medium risk stock paying out 10$ is worth about 100$ which gives you a nice 10% yield.
If the stock suddenly gave 20$ the stock price would quickly shoot up to 200$.
Bitcoin inflation with the current reward is ~26% so even at steady prices like now the total BTC value is increasing 25% per year.
When that inflation halves the effective yield of BTC goes way up, 12.5 percentage points, to adjust to that the price has to increase.
Why would the market be surprised?
1. 7200 BTC are created each day if 10% of that is immediately sold for $ then the reward drop leads to an immediate ~2% shortfall of BTC at mtgox which leads to a rally.
2. People valuing BTC will buy at some
constant rate, like at each paycheck like myself - since the rate is usually going up, whenever we can. Even if I knew with 1000% certainty that BTC would be worth 1000$/BTC tomorrow I would NOT be able to vastly increase my buy rate.
So with constant value going IN short-term and supply sharply dropping short-term a 2% rise is near guaranteed to be a shock event. A 2% upwards shock could easily trigger a upwards correction.
Add to this deduction that alt chains experiencing reward halving DID see a price
doubling - the reward change was no surprise on those alts either.
So to summarize, both logic and empirical data suggests a market shock will happen. Just because it is expected doesn't mean you can prepare!