In Australian Senate elections, why isn't the quota recalculated based on exhausted votes after each count?

In order to make sure the 2010 election was what I remembered it, I reviewed the AEC full distribution count for NSW Senate seats. I noticed that between counts the

quota = (valid votes / (positions + 1)) + 1

isn't recalculated despite exhaustion.

1. Ought it to be by Australian law?
2. Does simplifying this make counting much easier?
3. Is there a case where failure to recalculate quota will result in elected candidates returned being different?