Interesting article, though I think it incorrectly leaves the reader thinking that there is some interesting informating hidden in the average spacing of the numbers. In fact, all you need to know is that maximum observation and the number of observations. Once you simplify the average spacing goes away.

If M is the maximum serial number of N is the total number of observations, using the formula in the post:

    M + (avg. spacing) = M + M / N - 1 = (N + 1) / N * M

To me that gives a more clear picture of what the unbiased estimator is doing: inflate the maximum value by a factor that limits towards one as the sample size grows.