Modern PhD vs ancient Kings

Think modern central bankers and economists and PhDs are better managers of our money than their counterparts who lived 2000 yrs ago? Think again. I have compiled a few examples. It's difficult to get data from ancient times but what I got so far is striking. 

(rough estimates of currency value vs real goods):
US Fed -> 1913-2011 (abt 100 yrs). The USD has lost over 95% of its value 
Singapore MAS -> 1970-2011 (abt 40 yrs). The SGD has lost over 90% of its value 

UK BOE - 1900-2011 (abt 100 yrs). The GBP has lost over 98% of its value
Swiss SNB - 1945-2011 (abt 60 yrs). The Swiss franc has lost over 65% of its value

Info on ancient price systems are hard to find, but here're 2 of them:

Roman Republic - 3rd century BC-1st century BC (over 200 yrs). The Silver Denarius maintained 100% of its value.
Byzantine Empire - AD 498 - AD 1030 (over 500 years!). The Gold Solidus maintained 100% of its value.

Of course, eventually, these currencies also failed, for the same reasons as all currencies after that: Debasement.

In our modern world, it's called Money-printing (or more euphemistically - "Quantitative Easing", "Operation Twist", "Lowering the interest rate", "Currency devaluation to help exports", etc). Why debase money? Politicians over-promised and overspent (along with other reasons due to the intricacies of the modern monetary system).