I think that the umpires were guilty of following a 'rule of thumb', rather than the actual law of the game.
As an analogy, when deciding whether to award a free-kick (or penalty) for handball, football referees are often advised to decide whether the ball struck the hand or the hand struck the ball. While that's a useful 'rule of thumb' the ultimate decision should only be made based upon whether the contact was 'intentional'.
I can recall one inter-county match I refereed where a defender, inside the penalty area, could see that the ball was heading for his arm and stood stock still, allowing it to do so. He was none too pleased when I awarded a penalty (on the grounds that the contact was intentional). He was working on the 'rule of thumb', whereas I was working to the actual rule in print!
Similarly, when a cricket ball makes contact with the hand of a batsman (leading to an appeal for 'obstructing the field') umpires are again advised to decide whether the hand struck the ball (i.e. 'Out) or the ball struck the hand (i.e. 'Not Out').
However, once again the 'rule of thumb' doesn't always tie in too well with the actual Law, which states that the obstruction must be 'wilful' in order for a batsman to be given 'Out'. In this case an instinctive reaction has (wrongly, in my opinion) been deemed to be 'wilful', solely because the hand struck the ball, rather than the other way round.