For most IRA/401k savers, they are de facto dollar-cost-averaging, which is putting every new dollar to work in their policy portfolio. No harm in having them keep their nerve.
For others already possessing their zillions, you run into a different problem: are the prospective gains to be made by dollar-cost-averaging enough to override the opportunity cost of sitting on cash (which the less affluent saver doesn't have to worry about)?
Thanks for expounding. Maybe I'm missing something, but I still don't entirely follow.
Normal investors are only dollar cost averaging if they keep putting their incremental investment dollars into the same vehicles (or asset classes, or whatever). And whatever the size of your portfolio, putting money into securities makes sense only if the expected return exceeds other options (holding in cash, paying down debt, starting a business, buying lottery tickets, whatever).
Certainly if you're rich it can be a bit easier to diversify. And there are probably certain opportunities available to you (real estate deal with $100,000 minimum buy-in, for example) that aren't realistically available to other people. But the basic calculus of whether to increase your investment in an established position (even if that position is cash) or open up a new position is the same.