Words like "surely", "definitely", and "price going to double" mean nothing - they have no fact and little analysis behind them. It's pure speculation. And if you read posts from June of this year you'll find a bunch of people claiming that BTC is "surely", "definitely" going to increase by the end of 2014. What's happened in the last half of 2014? The price has dropped in half.
The halving of BTC mining presents a good idea to further explore as it get's closer to 2016 but NO ONE should be declaring the idea puts any certainty on price increases.
Businesses are adopting Bitcoin as a payment option so they can appeal to more buyers, but they aren't then holding their Bitcoin and using it buy the goods and services they need, they're exchanging it immediately to fiat currency - which is more stable and universally accepted. This immediate selling of Bitcoin supports the downward pressure and keeps prices for Bitcoin low and stable.
I think that many people who are long term bulls aka permabulls aka people who are hodling would put some value into "surely" as this is what they think will happen
There is a big supply of bitcoin in the hands of goverment from raiding places like Silk Road too that gets put in the market eventually.