But Murdoch can steer the board and the board can steer shareholders up to a point. If Murdoch and the board say, "We are recommending this offer because of X, Y and Z." many shareholders will go with their recommendation. And again, it's a matter of Comcast can do it, but it requires more.
If the sale is approved by the DOJ and the board has recommended the Disney bid, Comcast will have to offer a substantially higher bid to make shareholders go against the board.
Under normal circumstances, a 10% higher bid should be enough to shake things up. If the deal has been approved and the board says it's the best course, Comcast would probably have to go 15-20% higher than Disney to stay in it.