I think the idea is to include a small independent stats package not a full featured still developing third party. Any number of people need std dev easily and reliably available. If you need numpy on top of that, you know you do and can afford the effort.
For 99% of my work numpy and the associated compilation overhead is unneeded - fits my brain, fits my needs
So let's amortize the cost of compiling and/or installing fast binaries by only relying on plain Python.
It would be great if there was a natural progression (and/or compat shims) for porting from this new stdlib library to NumPy[Py] (and/or from LibreOffice). (e.g. "Is it called 'cummean'")?
For 99% of my work numpy and the associated compilation overhead is unneeded - fits my brain, fits my needs