They call it a “plugin development kit”, but what it really means is that developers can write compiled C/C++ apps for WebOS now. And according to John Paczkowski:
Perhaps more important, the PDK will allow developers to rewrite
mobile apps created for other platforms to run on webOS with
minimal modification. Apps that currently run on Apple’s
iPhone, for example, can be ported over in a matter of days,
sources close to the company tell me, and they don’t really
suffer any degradation in performance.
I can only assume that this is in reference to games with cross-platform cores, not utility-type apps that are Cocoa Touch through-and-through.