Cuts both ways nev - the reason you get asked is because 90% of the time if the aircraft is looking early it's because they are. You might have nailed your time but what about the guy you're following? Or the one three ahead? What about when the one with max does better than expected? Do you want us to just leave a 3 minute gap behind him or would you rather we speed everyone behind up a bit to fill the gap and save 60 or 90 seconds each?
How many times am I told by an international heavy that they can't possibly lose 5 minutes from 250 miles out when I know they'll lose 4 minutes on profile? Regularly. Or they're early and when asked their speed the response is "280" or "300"? Again, a regular occurrence.
The sequence isn't set in concrete - the flow times are to put you in about the right place, not to space you to the nearest metre down final.