The article mentions, "REE 2011.03, which is Ruby 1.8.7 patchlevel 334". Not sure if this was a recent edit or not.

ree is 1.8.7 - Rails3 doesn't work with anything below 1.8.7

Interesting, IIRC Rails 3 works best with 1.9.2 I'm going to run the benchmarks on 1.9.2 vs. 1.8.7 and see how they fare.