dear Monkenstick,
"I checked out this figure and apparently you have it from Dr Theobalds site of the talkorigin. I once had a discussion with Dr Theobald on cytochrome c incongruence and I have to admit that he is the best defender of evolutionism I've ever met in my entire life. I guess it is his full-time job. However, as mentioned before the cyt c incongruence could never be compellingly conluded since the Stellaria genome hasn't been sequences. So long it hasn't been sequenced I simply claim the stellaria cyt c incongruence as proof against common descent. By the way, he wasn't able to beat the IL-1 beta incongruence, neither the redundant src kinase family"
This on the side. Now, with respect to the graph. A more fine tuning analysis of the figure may reveal two graphs that demonstrate overlap. In fact, there is some evidence for that if you have a careful look at the graph between 0.4 and 0.5 (x-axis). It may implicate the existance of two types of mutations.
Best wishes,
Peter