The problem with your statement is that there may be a new digital currency that displaces Bitcoin ... namecoin, anycoin, litecoin, dogecoin. Maybe not one of those, but a 2.0 of some sort that attracts the miners.
If a NEW Bitcoin equivalent takes the spotlight and Bitcoin miners retrofit their rigs to mine for the new network, then someone that had put all of their money into Bitcoin could lose it all.
Nothing guarantees the continued use of Bitcoin. It is a decentralized fiat currency.
It's entirely conceivable that in the future there are half a dozen or more crypto-currencies out there that provide different qualities that make them more or less fit for use by different groups of people.