Python does has a nice clean grammar if you have to generate code, but yeah, if they already had a Weka model it's not clear why they aren't just evaluating that in a JVM. The only exotic thing they're doing is calling a Python module that can read Win32 portable executable files, though there appear to be similar Java libraries. Maybe they want end users to install and run something, so they avoided requiring the huge download footprint of a modern JRE?