The calculation is on the number of owners actually voting (or their unit entitlements if a poll is called). A non-vote is exactly that. It’s not a yes vote and, in fact, usually helps the “no” side because it makes it easier to reach the 25 percent of a reduced figure. And before we get into it, an abstention is not a vote – it’s a declaration that you aren’t voting, so it can’t be counted in the overall percentages.
And just to clarify the final point, the calculation is based on those actually voting (or their unit entitlements). This is what the Fair Trading website says: “A special resolution is passed if at least three-quarters of the votes cast support it.” That’s ‘votes cast’ not voters present or owners.