"Is this a basically accurate assessment of the legal differences between GRZ & KRY that may explain Venezuela's willingness to allow GRZ to go the arbitration route?"

No. As I explained to wookie in a PM there is no difference between the two in terms of the legal basis and core arguments. They are both based on impairment of an investment under the BIT. Each has different facts, but the only significant factual differences will be those that relate to damages.

Unfortunately, the law generally and for BIT arbitrations specifically do not necessarily follow common sense understanding. The evil actions of Hugo are pretty much irrelevant, as only the impact on the investment matters. There is no concept of punitive damages, only expenses and lost profits. The damages that will be awarded also do not depend on what Venezuela does with the property following the onset of arbitration.