A few songs I submitted in current times received scores significantly lower than when I submitted them a little over a year ago. There is not much we can do to change the zero-bombing, but there is stuff we can do to detect it and help prevent its effects.
First, make the number of votes per score visible for each song. e.g.:
5: 1 vote
4: 0 votes
3: 0 votes
2: 0 votes
1: 0 votes
0: 15094 votes
This facilitates actual "zero-bomber" detection.
Second, make it a requirement for a person to listen to an entire song before being able to rate. After all, if they haven't listened to the entire thing (or at least turned the volume down while they waited for the song to finish) then they shouldn't be qualified to rate it.
Third, make the "zero" vote count less for those users who consistently vote zero on songs, because there is a greater chance that they are zero-bombers than people who only occasionally vote zeros. A similar voting system has been implemented on IMDB, where the votes of people who consistently vote 0s and 10s count less whenever they vote 0s or 10s respectively.
Fourth, although this may be pushing it a bit, restrict voting temporarily (e.g. a few days) for those who consistently zero-bomb; this acts as a clear consequence to their zero-bombing behavior.