The difference, of course that in 1991, we were in a secular bull market (indices rarely stayed under the 200 DMA and most of the retrenchment were stopped there or just above). During secular bull markets, one should expect longer periods of "overbought" than in bear markets just as in secular bear markets we get longer periods of oversold. Unless you are taking the position that the secular bear is over, or that we have an interim cyclical bull starting here, more recent experience (the last three years) should weigh in more heavily in this series of indicators.
Zeev