> FWIW, the very first thing that I checked was the dependencies of pythonw.exe

The version in the Store has a different build of pythonw.exe (because it has to be able to determine its user site-packages location differently).

Dump of file C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.7_3.7.1520.0_x64__hd69rhyc2wevp\pythonw.exe

File Type: EXECUTABLE IMAGE

  Image has the following dependencies:

    api-ms-win-core-libraryloader-l1-2-0.dll
    api-ms-win-core-com-l1-1-0.dll
    api-ms-win-core-errorhandling-l1-1-0.dll
    SHELL32.dll
    python37.dll
    MSVCP140.dll  ****** bug here, but already fixed for next release
    VCRUNTIME140.dll
    api-ms-win-crt-runtime-l1-1-0.dll
    api-ms-win-crt-environment-l1-1-0.dll
    api-ms-win-crt-heap-l1-1-0.dll
    api-ms-win-crt-math-l1-1-0.dll
    api-ms-win-crt-stdio-l1-1-0.dll
    api-ms-win-crt-locale-l1-1-0.dll
    api-ms-win-crt-string-l1-1-0.dll
    api-ms-win-core-handle-l1-1-0.dll
    api-ms-win-core-synch-l1-1-0.dll
    api-ms-win-core-rtlsupport-l1-1-0.dll
    api-ms-win-core-processthreads-l1-1-0.dll
    api-ms-win-core-processthreads-l1-1-1.dll
    api-ms-win-core-debug-l1-1-0.dll
    api-ms-win-core-profile-l1-1-0.dll
    api-ms-win-core-sysinfo-l1-1-0.dll
    api-ms-win-core-interlocked-l1-1-0.dll
    KERNEL32.dll
    api-ms-win-core-winrt-l1-1-0.dll
    api-ms-win-core-winrt-string-l1-1-0.dll
    OLEAUT32.dll
    api-ms-win-core-winrt-error-l1-1-1.dll
    api-ms-win-core-winrt-error-l1-1-0.dll