These two functions are right on the boundary edge of what the statistics module is trying to do, """The module is not intended to be a competitor to third-party libraries such as NumPy, SciPy, or proprietary full-featured statistics packages aimed at professional statisticians such as Minitab, SAS and Matlab. It is aimed at the level of graphing and scientific calculators."""

It is debatable which side of the boundary they belong to. MS Excel has both of these functions, but it isn't a given that a scientific calculator would have them.

Also, the current functions require only high-school level knowledge, but these two require more skill to learn, use, and interpret.