Which rule exactly? There are a number of rules interacting which make buybacks in the US better right now, it's not just a rule that says "buybacks will have b

Which rule exactly? There are a number of rules interacting which make buybacks in the US better right now, it's not just a rule that says "buybacks will have better tax treatment than dividends". The dividend tax rate could be changed to zero tomorrow (or the tax treatment on dividends could become like other countries who don't double tax) and buybacks would be less favorable. Taxes are complicated, there will always be one choice which is better than another from a tax perspective.