You, and many others, seem to imply that being "bad math" (mathematically not sound) is the same as being "bad" (in the broad sense). The author never said that the method was useless, nor anything similar. PageRank was an obviously great advance at the time, but this does not mean that it can not be improved.

Now, if you accept that it can be improved, the author has a great point: trying to understand the role that this made up constant plays in the algorithm (and getting rid of it if possible) is a clear path to what might be an improvement.

Oh, and "physical constants" are not even remotely similar to using a made-up constant. Physical constants are measured experimentally, meaning that they "exist" in the object that the mathematical model tries to explain. Now tell me how do you measure ".85" being an "existing" constant in the "ranking of website importance" object that pagerank tries to model...