Sadly, being right is not always enough.The whole point of the Brown U-turn is that he was not right. He had been knowing telling the public untruths about what his government would do, in order to create one of his beloved 'dividing lines' between Labour and the Tories.
Incidentally this just confirms what has been obvious for a long time- Gordon Brown is the Wile E Coyote of British politics. He is an inveterate schemer but utterly useless at it. He thought it would be a brilliant wheeze to seize on Andrew Lansley's comments about there being a necessity for cuts by pretending that there wouldn't be cuts under Labour. The plan was always going to backfire and leave Brown looking dishonest when he made the claims and feeble when he was forced to back down. He also squandered a potentially effective approach for Labour- making the debate be about whom the public trusted to make the necessary cuts.