Most bowlers who get wickets don't go for runs: sure, there's a difference between a bowler like McGrath who builds pressure by keeping it tight and a bowler like Donald who built pressure by always looking likely to take wickets... but for all that Donald would serve up the odd loose delivery and present scoring opportunities... he still ended his career with an economy rate of 2.83!

Sure... if a bowler is consistently beating the bat you don't mind the odd boundary... but that still needs to be within reason: 5/155 off 25 overs in a low scoring game is likely to concede the match in a way that 3/60 off 25 overs will not!

To compound matters... 5/155 one week could easily be 2/155 another week.... which is catastrophic... but 3/55 one week becoming 1/60 the next means the bowler has still done his job.

On those two weeks combined... the "strike bowler" ends with a wicket every 50 balls... and the "tight bowler" ends with a wicket every 75 balls... but the former ends with an average of 51.67 and an economy rate of 6.2 whilst the latter ends with an average of 30 and an economy rate of 2.4!