The price of gasoline cost $0.25 SILVER per gallon a century ago, and it still costs $0.25 SILVER per gallon today. The rise in apparent price is due entirely to local currency fluctuations.
Silver and gasoline are industrial commodities that are both manufactured: both have to be taken from the ground and refined. Both have storage and distribution infrastructures. Not only have all these systems radically changed over the last 100 years, the relative scarcity and demand for silver and gasoline have not remained constant. Your point seems to be that the inherent value of commodities never, ever change with respect to each other, even over a hundred years. That doesn't seem to be true. Just choosing a commodity to be a currency would change it's value a lot.
Because BitCoins are not directly tied to any single currency, and are not manipulated by fiat, and are instead a representative of time and number of users, BitCoins will likely become a far more stable monetary unit than government-issued currencies. When you see the exchange rate graph of BitCoins begin to mirror the price of oil, that day will have come. If you look at the 1M graphs of BitCoins and oil, that mirroring has already begun.
My God, why would you want your currency tied to the inherent value of oil? I hope for your sake that's not true. One exocet later...
Dollars at least have the advantage of being the fiat currency of the most wealthy and powerful national economy on earth, if only being backed by it's national debt. Bitcoins are the fiat currency of some internet geeks and drug addicts, and are only backed by the strength of... the bitcoin market. As long as everyone has "faith in bitcoins", you're good.