Tanking asset prices

If you have more sellers than buyers, more supply than demand, prices fall. Will that happen as baby boomers retire? Here's the case:

At the core of concerns about the baby boomers' retirement is something economists call the "life-cycle hypothesis" of economic behavior: Most people tend to save little when young, build up savings during middle age, and then spend those savings in retirement.

That leads some savvy analysts to fret that the boomers' retirement will be marked by widespread selling of stocks and bonds. Jeremy Siegel, a professor at the University of Pennsylvania's Wharton School, has said his computer model shows that, absent help from overseas investors -- buying he does expect to cushion the blow -- the boomers' retirement could cause stock prices to fall 40% to 50%.

I've read stories with the same hypothesis in the past, but not just for stocks but for all asset classes and it's a little frightening. I'm just an armchair economist, but I don't think this catastrophe will come to pass. However, I am trying to diversify into non-U.S. and non-European assets.