Is there documentation more complete than the "more information" link in the Lifetime Planner?
It's possible to bootstrap a meaningful distribution using the individual's data in Quicken and historical investment prices, inflation, actuarial records etc. That would be a valuable addition to Quicken. Moreover, it wouldn't be terribly difficult to provide such a probability distribution.
Forgive my cynicism, but the absence of details in the "more information" link and the fact that it's presented as a three-line graph instead of a distribution causes me to think this is a toy to give naive users a false sense of future certainty and an inflated sense of Quicken's planning value.