Merchant: "Bitcoins eh? New fangled payment system that cost next to nothing to implement? Overseas payments n all? Sounds amazing. What are these bitcoins worth? 20 Dollars each?! Wow thats amazing.. They went up how much in value in how little time?
Scenario B
Merchant "Bitcoins eh? New fangled payment system that cost next to nothing to implement? Overseas payments n all? Sounds amazing. What are these bitcoins worth? 2 Dollars each! And these can be changed relatively easy into dollars?
If a new merchant is taking a risk on accepting payments the psychological impact of only getting 1BTC instead of 10BTC for an item costing 20USD is immense. This is why I think its better poised for adoption by merchants now more than ever.
Scenario B fails to include the fact that the first thing your average merchant will do when seeking to set up a new business would be to pull up news stories on the currency and immediately see "Bitcoin loses 90% of its value in 3 months." This likely won't be followed by any positive stories unless the price shoots up in a short time frame again. That doesn't make for an attractive payment platform for new merchants.
I do agree with one point in the other comments though - Bitcoin's value runs much deeper than its day-to-day price. The issue is that the fluctuations are deterring average merchants from jumping on board right now.