> recursive descent parsing

The parser is Java, actually. And it's not recursive descent.

> tasks well suited for it

Fancy that! Using a language for things it is well suited to! :)

> compiled and JVM languages stitched together with Mathematica

A lot of stuff is still WL though. Data curation, evaluation, scanning, typesetting, formatting, and, you know, the actual computation in doing something like http://www.wolframalpha.com/input/?i=regression+of+literacy%...

But it seems like you're complaining the backend isn't written in Wolfram Language? The JVM is great at that stuff! I don't call that ball-of-mud at all, just using the right tool for the job.