Why is it that when the chasing team wins, they are said to win by the number of wickets remaining?
What is the relevance of this? You could have 10 wickets remaining and reached the target on the last ball of the last over - it would've been a close game but the margin would've been the greatest allowed.
Wouldn't it make more sense to describe the margin as the Net Run Rate (which is what is actually calculated in the World Cup group ladder anyway) or the number of overs remaining?
Largely, this is historical. In the days before one-day cricket, matches generally were won and lost on the number of wickets taken in the fourth innings - it was a rare match which ended up with more than one team likely to win as the match approached its end, but rather a question of whether the team in the winning position could force a win, or whether it would end up as a draw.
Obviously that's changed with the advent of one-day cricket, but there certainly are still matches were number of wickets is important; take for instance New Zealand vs Scotland in the 2015 World Cup - if New Zealand batted out their 50 overs, they were going to better Scotland's total of 142 so "won by 3 wickets" probably is more appropriate than "won with 151 balls remaining". I agree net run rate is potentially a useful measure of the margin of victory, but I suspect trying to explain it would confuse people who aren't hardcore cricket fans so much that its value would diminish beyond the point of usefulness.
Think of it as having "resources". In the first innings, the batting side accumulates resources in the form of runs - 300 for 1 is the same as 300 for 9 in resource terms.
The side batting second then has 10 wicket "resources" to accumulate the target score.
Hence if the side batting second wins, it's because they marshalled their resources properly, to maintain them and achieve the target.
A result is usually described in terms of runs or wickets, but for limited-overs games the number of overs taken to achieve the target is normally mentioned too.
Describing it in terms of NRR might be logical, but it's not the tradition, and cricket is all about tradition.
Incidentally, this approach of resources is what underpins the Duckworth-Lewis method.
ODI's can never result in a draw, unless weather prevents the minimum overs to be bowled, and therefore the number of wickets in hand at the end is really immaterial. This is because, unlike Test cricket, the match is won, lost or tied on whether the 2nd batting team reaches the target in the number of overs allowed. (i.e. a team can still lose with all 10 wickets in hand.) Their win should be measured in overs or balls remaining or their loss by the shortfall in runs. Tests, on the other hand, are only won by bowling the other team out twice (notwithstanding declarations), and so the number of wickets in hand or excess of runs is the relevant measure of a win.
