Matt, I should mention that I made a typing error in my example above, having stated the dimensions for the second turn were the same as the first. They are not and are corrected in that post.
I followed your math, but don't see that it supports your quote above, as stated. Taken literally, we could simplify the example to remove the turn and say we're riding the same 1,000 feet of straight road. If we make a pair of passes, one at 50 and the other at 51 mph, the difference in the time it takes to cover the 1,000 feet is .27 seconds. If we make a pair of passes at 100 and 101 mph, the elapsed time difference is .07 seconds.
For your statement to be true, the distance covered must be proportionally larger. Your math allows for this, but the opening statement doesn't seem to.
That statement is only true in the context of the situation you presented, a constant radius turn at a defined speed and lat acceleration. These two values determine the radius and length of the turn. Of course, on a straight road the distance is the same for different speeds, thus the difference in elapsed time varies inversely to the speed.