I believe that 'stat' is an applet available in BusyBox which has so far been left out of Core. I wonder whether it could be included in the future (i.e. added at the next rebuild of BusyBox).
I reckon it might be rather useful to have it in the base (without adding too much "fat") instead of needing the whole 1.7M of 'coreutils.tcz'. But that is just my view ...