Re: When payout per block halves, how will that effect difficulty?

Difficulty will only drop if a lot of farms turn off their gear. It's likely that most folks will be mining at a loss for the first period after the halving. What sucks is, since mining only alters the total supply by a fraction at a time, the supply/demand curve won't be moved very much at all by the halving so it won't have much effect on the exchange rate.

Using the same argument, why don't you think that most of the miners are alreayd giving up(looking at the low prices ) ?
Shouldn't we also expect a drop in difficulty right now ?

https://blockchain.info/charts/hash-rate This doesn't seem to indicate that.

Shouldn't the hash rate actually go down knowing the sites like C_Cex shut down mining.
I expected to see a drop in hash power as well.

CEX.io shutting down payments because the maintenance fee > earnings is not the same thing as the gear being unprofitable to run at all. That would only be the case if the maintenance fee they charge per GH/s is their actual cost.

I would say that it would be fair to say that cex's maintenance fee is roughly in line with their actual costs. I am sure they are/were making a profit off of their maintenance fees, however I would think their margins were pretty thin.

Additionally it would be a good guideline even with a small profit as miners would not want to keep their machines on just to essentially break even, they want to expect at least a small profit after costs to account for the risk they will have bad luck