Is it just about margin, though, or is it actually percentage? If the latter, the same margin can be worth a different amount, ie a 10-5 win is 200% but a 90-85 win is only 106%.
Which makes the complaints about the Illawarra game on NZ's behalf odd, because a 65-52 win got them 125% but a 99-86 win would only have got them 1.15%, so the longer the game went the more they would have had to increase the margin for the same percentage benefit.
Similarly, if it's overall margin a win increases it, no matter the margin. If it's percentage, a win by less than your average winning margin will actually decrease it.
For example Sydney's percentage is 106.44, with their points averages being 94 for and 89 against. If they beat Illawarra 91-90, their percentage drops to 106.25.
Melbourne, NZ and Brisbane are all so close to 100% there's not that much wiggle room for percentage-decreasing wins, but it can happen.
In Luuuc's example, the 100-75 win would give NZ a percentage of 102.52, while a 95-90 Melbourne win leaves them on a percentage of 102.50, and NZ goes through.
However, quite a few people are only quoting margins on Twitter, and if that is indeed the tiebreaker a) it unfairly punishes slower-paced teams and b) all this math becomes irrelevant.