I think it's just the rule of odd numbers. Like in decorating, odd numbers are inexplicably more eye pleasing. There are 4 stone bands but to me they do not look 'right' while at the same time I can't think of anything that is wrong with them...just that I like 3 or 5 stone better.
Strangely, the odd number rule also applies to Star Trek movies. It is generally accepted that the only the odd ones are worth seeing...if one is inclined to watch Star Trek movies at all.