Earlier quoted context omitted.
With the 40+% drop in 2008, I'm not sure that the 100-year average for American stock market/broad-indexes is still over 8%-per-year.
Over that time scale a 40% drop is not that big a deal. 1.08^100 = 2200 so 1$ = 2200$ (2200 * .6)^(1/100) = 1.0745, and 1$ = 1320$ PS: A 40% drop might seem like a huge deal but over time it's just not that important. ~8% vs ~7.5%
On a 100-year scale, a 'tiny' 0.5% drop in compound return is massively 'important' in effect. It's no consolation to the person with 40% less money that his annualized performance was only 0.5% worse; you own the $1320, not the 7.45%.
"8%" is often thrown around as a long-long-term guesstimate of stock returns; if in fact that's slipped to 'merely' 7.5% based on the last year, that's remarkable.
The hit against the annualized rate within timeframes more like the earning careers (or even lifespans) of News.YC readers is also big. Here's an interesting graph for S&P total return over the last 20 years:
http://mahalanobis.twoday.net/stories/5279642/
A dollar from 1988 was giving near (or far over) 8% annualized return until mid-2007; now it's more like 5%.