Noone really believes this to be true all the time.
Obviously the amount of water it takes, wind or sun drying out a track, the way its graded, etc etc all can make figure making and splitting variants just about the hardest thing for any figure maker to do. Doesn't matter whether its Beyer, Rag, or Brown this is VERY tricky.
I just think that ever since the Valid Video/Shake YOU Down incident that people have really questioned variant splits, especially when they happen with two races run about an hour apart on the same track, with no weaher changes. That incident may have been the worst blown split variant I ever saw. Which of course is going to happen to anyone who makes figures long enough and often enough, but the high profile nature of those two horses and their subsequent starts really made that one ugly. Had it occurred with two allowance horses, noone would have really noticed much.
Anyone who doesn't realize that we are talking about a very inexact science when we speak of speed figures really doesn't get how hard they are to accurately make, or how much time and effort goes into making them by any of the top guys.