Ok, I have learned why the PiperSport is not certified at night.  It actually has nothing to do with the LSA cert.  The Czech sport aircraft (which Piper bought and relabeled), is certified at night.  However when Piper asked the FAA to cert it as the PiperSport, they noticed the white navigation lights (which are wingtip mounted instead of on the tail) are not completely visible from directly aft, due to the shape of the wingtip.  There is talk of a fix, basically a white led mounted on the tail, which would remove the night restriction.