Well, that graph says nothing about international exchange rate, just the purchasing power has dropped in the last century. The steady decline is mostly an indication of growing wealth across the whole populace. All you can really garner from just that single graph is that the people have gotten more wealthy, hence less purchasing power per dollar bill. If you start reading too much into it, you'd think everything was going downhill since the Great Depression.

If the value didn't drop while wages increased, then everyone in the country should be living in mansions right now. The best way to stop the decline in purchasing power is to stop wage increases.