Adam's plan to create a store that offers a discount for paying with BTC is a result of the deflationary nature of BTC. But ware he's sees this as a good thing it is in fact a very bad development (not his fault of course, he is just doing the logical and inevitable thing under deflation). As a merchant he is essentially trying to race ahead of the deflation rate, this will inevitably result in an acceleration of deflation, just as in a inflationary environment the merchant is trying to raise prices and race ahead of inflation and this creates even more inflation.
When the bulk of merchants adopt this kind of pricing strategy (as they inevitably must in a deflationary environment), the result is to drive more deflation as the 'discounts' now effectively become the true value of BTC, exchange for USD will try too catch up but because these discounts will most likely be by a percentage they will remain forever above the BTC/USD exchange rate and act to pull it upwards perpetually.
Now how do merchants ever actually make money if they are offering huge discounts? The only way for the merchant to close that gap is to hold BTC for a long enough period for the coins appreciation to put them back in the black (or just accumulate private hoards). Now ignoring all the risks they now have of a crash in exchange rates the merchant now has very low turn over of money, this is effectively removing large portions of BTC from circulation which leads to yet more deflation. And no the higher rates of deflation won't decrease the time the merchant holds coins because the customers will demand an even deeper discounts, as the size of the discount needed to stimulate the consumer is proportional to the rate of deflation.
The logical end result is hyper deflation and the collapse of all commerce and investment.
You're assuming that things stay the same - The deflationary business model works during an actively deflationary environment, the discounts will vary based on the expectations of future value. Right now we're in a period of revaluation when things will happen fast, in a few years we'll have a much more stable pricing structure which will reduce the discount since there is less expectation of appreciation.
For example, right now if the price of BTC goes from 100 to 200, that is a 100% appreciation. If 1BTC is 10,000 and goes to 10,100 that is less than 1% appreciation. In the first situation, it makes sense to sell for a 40% discount, because the % growth makes that a good deal. In the second situation, you'd be an idiot to do that.
Get it? People change their behavior based on incentives
So that means that right now when the expectation is for incredible upside (tens of thousands) with very little downside (can only go to zero). That isn't true forever.