As far as I know: these REE releases/patches are for 1.8.7, a release of Ruby that isn't quite being actively developed, only maintained. Stuff similar to this is being folded into the official Ruby interpreter, which is now at 1.9.1 (1.9.2 soon!).

The uptake of Ruby 1.9.1 has been slow, and people are staying on 1.8.7 for compatibility reasons. Thus, these patches are trying to bring better memory performance to the old but widely used 1.8.7.