Under Windows R is installed, but its bin folder is not added to the
system PATH variable. I know that this is handled properly under *nix
like systems and I wonder, why this is not the default also for the MS
Windows? I guess that for most users a shortcut on the desktop or
anywhere else is sufficient, but there are occasions when one expects to
able to lunch R from anywhere - say the Command prompt.
This is the normal behaviour of Windows applications. There are several
reasons, including length limits on the Windows PATH (which are
version-specific) and that shells are not normally used -- most Unix
shells hash the path contents so lookup is (almost) independent of the
number of applications on the path.
Finally, those Windows installers that do add to the PATH frequently fail
to uninstall correctly.