A Sub-Two-Hour Marathon In 2038?

Everyone's talking about this Runner's World article about the prospects of a sub-two-hour marathon. I first saw the article on Facebook, via my Open Borders compatriot, John Lee. A few days later, Alex Tabarrok at Marginal Revolution reposted it with some mostly uninteresting discussion unfolding in the comments section.

I checked the comments section again this morning, and discovered a link to a rather fascinating (and short) blog post predicting that the sub-two-hour marathon will happen some time around the year 2038.
Inspired by Patrick Makau Musyoki's new marathon record in Berlin yesterday, I looked for trends in the marathon world records for each decade going back a century. I only included the fastest time in each decade. I expected a plateau like this, but I didn't expect it to be so neatly logarithmic....
Followed by:
A whole crop of articles commented over the last year onstatistically improbable sprinter Usain Bolt, who is ahead-of-trend by thirty years. In the same vein, looking at the marathon plot, we shouldn't expect a male human to break two hours in the marathon until 2038. And it's reasonably assumed that the incremental improvements we see in these times is a result of (decreasing marginal) improvements in training, nutrition, and running equipment.