OzPunter,

This is only the original nominations for the races. It's nothing out of the ordinary for there to be small fields at nomination time. In cases like that, what they do is extend the nomination deadline, and then they often end up with bigger fields. If you look here, that's exactly what they've done:

http://www.racingnsw.com.au/extendednoms.asp#12020

If there is still a race with only 4 runners after tomorrow's extended deadline, they may delete it. They do have 9 races programmed, so they could afford to lose one race, possibly even two. The final fields for Saturday's races aren't known until Thursday morning after acceptances.