Sorry, but I've not been able to locate anything (even on the official pages) informing me of the differences between the two versions.
Even a query on their official forum has been unanswered for many months -
The license page talks a bit about the "internal" differences
CKEditor Commercial License - CKSource Closed Distribution License - CDL ... This license offers a very flexible way to integrate CKEditor in your commercial application. These are the main advantages it offers over an Open Source license: * Modifications and enhancements doesn't need to be released under an Open Source license; * There is no need to distribute any Open Source license terms alongside with your product and no reference to it have to be done; * No references to CKEditor have to be done in any file distributed with your product; * The source code of CKEditor doesn’t have to be distributed alongside with your product; * You can remove any file from CKEditor when integrating it with your product.