Regarding the graph, gas prices, and the larger picture:
I agree with Ed regarding the historical downward trend in gasoline prices, especially if we are talking about a 100 year time window.
Most of us are not.
The graph from 1918- 1960 is pretty irrelevant to any discussion. In 1918, the petroleum industry was in its infancy and was essentially a monopoly. Even price data from 1960- 1973 has limited utility in the discussion, because that was all pre-EPA - pre-unleaded fuel, and pre-modern economy in a lot of important ways.
When most people complain about gas prices, they're complaining about the extreme volatility - the "knee jerks" that Bob notes, as well as the general "straight up" increases since 2002. There was a major dip that occurred around 2010 with the advent of fracking, but fracking is the nuclear power of our generation - the environmentalists' sum of all fears. There is still great pressure to stop it.
The graph also has no recent data. I think the point most people are making is that the current average price is at or over the peak of the graph ($3.50/gal), meaning that it's 30%-50% more than it was a couple of years ago.
Obviously, everything has to be viewed through the lens of the general rate of inflation, and that's been my point in trying to sound the alarm regarding real (as opposed to "measured") inflation. In the places that matter most, the cost of goods i accelerating pretty dramatically. Will it slow or stop? Not as long as the Fed is buying bonds and keeping interest rates at near zero. Will the price of gasoline return to earth? Not as long as we make it harder and harder to extract, transport, and burn with policy and treaty.
Whether or not this is a good thing is politics, which I'm trying hard to personally forswear on this site, but it's got to be fair for old men (many of whom are on fixed incomes or money they saved when it was worth a lot more) to complain about the price of gas, which is after all, the great American pastime.
Regardless, as Jim notes - driving a Speedster remains pretty cheap therapy.