Ann: DOW: Presentation - Offer for Spotless & equity raising, page-82

That's not technically true - the restriction at 20% applies in the absence of a takoever offer. They have made one, so they can go above 20% (obviously that's what they are trying to do). However, they won't buy on-market due to the structure of their offer. I posted somewhere already as to why they will stop at 20% - in short they have their blocking stake now, there is no need to spend more capital unless they get full control.