Hello!
The use case here are buffers like comint or IRC chat buffers. It's nice to keep the last line of the buffer flush with the last line of the window, to show the maximum amount of data. (recenter -1) at the end of a buffer is supposed to do just that. In this case, it does not, but instead leaves point in the *middle* of the window.
If it is not possible to display that line halfway (which sounds like a missing feature to begin with), I would expect Emacs to least try to leave point as low in the window as possible, instead of in the middle of the window. C-l likewise won't move point any further down, for example.
Regards,
Jorgen