2. Many people use the USD as a reference, but what if the USD collapses? It will likely pull other fiats into inflation as well, so the reference might as well change to something else like gold.
The bitcoin purchase power can only increase overtime, but should be lower and lower increases, it would eventually get nearly stable but who knows how many years that would take, maybe a century or two...
USD can easily be replaced by EUR or even JPY if it's the case.
The point is different: as long as governments stick to their own currency, they won't accept the outsider.
While you, and me, and some businesses can use Bitcoin as standard (after the price stops fluctuating wildly), but governments won't.
And again, if you'll want to buy goods and services the starting price will be in the currency of the country the shop resides in. Then it can be derived to Bitcoin and others.