I brought this up in the Lord's test match thread, and thought it'd be a good discussion.

Essentially, I was wondering about the 'impact in line' rule. Assuming the ball pitches in line or outside off, and the batsman is playing a shot, why does it matter where the ball impacts the batsman relative to the stumps?

To my mind, it seems to me that if the ball impacts outside off but is still going to hit the stumps then it is still bad batmanship and the bowler has sufficiently deceived the batsman, and a wicket should be taken.

This isn't quite the same as the 'pitched outside leg' rule, because I can see the merits of the argument that that rule discourages negative bowling. But impact in line? Does it perhaps give too much advantage to the batsman and he or she has been genuinely deceived?