Exactly right - BlackRock and other large indexers have no legal obligation to follow the recommendation of an independent adviser (like ISS, Glass Lewis) in a proxy contest, even for a passive fund. In most cases they passively anticipate the index provider's (S&P, Russell, MSCI, etc.) moves for corporate actions, but management elections for the board and executives are much more subjective as they don't influence the position itself (note that the manager can sometimes also be the index provider, like BlackRock = iShares). The smaller index managers almost exclusively follow the proxy adviser's recommendation because they don't have the resources to analyze board decisions for ~8,000 different companies.