The dollar is theoretically limited within the subset of United States currency while the concept of national currency itself is only limited by the number of nations on Earth.
Now to bitcoin.
Like the dollar the bitcoins are theoretically limited in supply. But what if bytecoin comes along, then gigacoin, followed by googlecoin and so fourth? There seems to be no limit on the number of bitcoin imitators possible.
While, like dollars, there might be a limited number of bitcoins within the subset of bitcoin, the concept of bitcoin is unlimited unlike the world’s various national currencies.
Competition will utterly devalue bitcoin unless it is adopted by particular nations to the exclusion of its competitors, however that is not to say that other nations will not adopt one or more of bitcoin’s competitors to the exclusion of bitcoin .. they most certainly would.
And how is that materially different from our current international system of free floating national currencies?
[Source: http://polifrogblog.blogspot.com/2013/08/is-bitcoin-really-any-different-not-in.html]
Do you know that the government can print unlimited money? They just need to press the "print" button.