I'm not sure how common it is in Australia but I know it does happen for some crops. I thought it would have been mostly an American issue with the way the agricultural economies function there. You buy the seed from Monsato or one of the subsidiaries and then you grow the crop to their instructions in many cases.

I spoke to my brother in QLD a few days ago and he lives in a country area that's an agricultural zone growing grain crops and he said it's just how it's done these days. Many farms are doing all they can to keep the banksters at bay, so if spraying with roundup pre-harvest would increase your yield it would be hard to resist if the numbers worked out.