Productivity growth in the U.S.

We are led to believe that this chart clinches the case for productivity gains in the US economy as a great, wonderful and continuing phenomenon.  Alas, the chart does not convince because the reference period is arbitrary.  Why use 1973-1995 trend as reference?  Especially since this was a period of abnormally low productivity growth as the author indicated in the text.  All one can reasonably conclude from this chart is that growth was higher both after and before this  period of low growth.

There may be other evidence to support this assertion; being no economist myself, I can't comment on those.

Link: Marginal Revolution: The U.S. economy in a sentence.