Would be more interesting to compare it against a realistic return from a savings account instead of saying "if the index is worth the same after 20 years then you haven't lost anything". You would have almost 25% more even in a 1.1% savings account.
A 1.1% savings account would have lost money due to inflation over 20 years. The author's methodology seems to subtract each year for inflation, so if he's comparing a post-inflation number year to year, and it's the same 20 years later, you've actually done much better than a 1.1% savings account.
I haven't seen a 1.1% savings account in the better part of a decade. Perhaps that's not useful to theorize about in the modern economic wonderland we've created.
If you look at it that way, it's also hard to theorize about stocks in that modern economic wonderland "we" (they?) have created. There could be, for instance, a large wave of defaults on the plentiful debt created by low interest rates, which is probably bad for stock prices, or else the trend of rising P/E ratios due to a lack of safer ways to get a return on an investment could keep inflating stock prices.
