When people talk about Bitcoin price, they usually refer to its price expressed in dollars. I really don't understand why...
US Dollar is going down in price, US economy is collapsing. There are many other countries which has more Bitcoin users, like Russia, China, Japan, Philippines and the whole Eurozone. Even ICOs are forbidden in the USA. It's not a so Bitcoin-friendly country, its national currency is not so strong. So why price Bitcoin in $?
There could be many other more appropriate currencies like EUR, CNY or RUB...
USD is the most stable fiat currency and giving a BTC to USD puts a price on bitcoins that the majority of people will be able to understand. If we were to give rates as "BTC to Gold" or "BTC to Silver" then people would have to go and google the prices for Gold and Silver and that would be even less convenient for people. Most people have some idea what the conversion of their local currency to USD is.
Yes I agree USD is still considered to be the most stable currency and not only that but also it's the only currency which has been popular all over the world since long ago and it's easily acceptable everywhere in the world. USA has a strong influence on most of world countries economies which even Euro doesn't have. Euro might be popular and acceptable in EU countries but most of Asian and African countries still prefer USD. So the people of a larger number of countries would prefer USD to BTC or vice versa to any other currency and that's why I guess this BTC to USD comparison and that's just fair I don't think.