Without wishing to upset anyone, one of the contributing factors is that the number of people reporting 160knts is often unrelated to the number actually flying the speed they report. If you don't fly the assigned speeds accurately how can we be expected to achieve any standardisation in final approach spacing?
Differences in ground speed of sixty knots and more is not that unusual between an a/c at five miles and one at eleven miles and as a Tower controller they are not many options when faced with anything over half mile a minute catch ups.