@Gordon Gekko
If you re-read the OP you will see that the outperformance of long-term US treasuries over a 20 year period is not without precedence. Nor is 20 years the longest period where long-term US treasuries outperformed US stocks (S&P500).
And that's just the US. Long-term government bonds have outperformed domestic stocks for periods of 20 years or more in every major industrial nation.
In any event, I read the phrase "almost any reasonable long-term period" as referring to the length of the period - not the frequency of such periods.
For the avoidance of doubt, I am not suggesting that bonds have frequently outperformed stocks over long time periods - they clearly haven't.
Nor am I making any prediction - implicit or otherwise - about the future performance of any asset class.