BitCoin is NOT a currency. Any business is rolling the dice accepting BitCoin with how volatile the price is. With how rapid the price swings (mostly down), no logical business would/should accept BitCoin. No different than gambling. To my knowledge my dollar last week is still a dollar today, not true with BitCoin, you would have taken a hefty loss this week only!
Your dollar is not actually the same dollar it was yesterday. It depreciated slightly in value (in fact, the major reason the Federal Reserve exists is to depreciate the value of the dollar in a stable way). In a year, most likely, your dollar won't be able to purchase the same amount of goods as it does today.
What you pointed out just means the dollar is merely more stable than bitcoin over the past few years. That may continue to be true tomorrow, next month or next year. Or it may not.