Are WTO dispute settlements "Law"?

From Simon Lester, yet another reminder for those studying tax treaty arbitration that the issues are many and difficult. When basic questions of enforceability can't be answered in an area of the law where things are fairly well developed and are subject to ongoing extensive public vetting and debate, it serves as a warning of what lies ahead for international tax dispute resolution. From the post:

There is some famous scholarly debate on whether WTO dispute settlement rulings are binding.  Here's a media take on it, from the CBC news (in the context of the Ontario feed-in-tariff case):  The World Trade Organization appears to have upheld a [discrimination] complaint against the Province of Ontario's green energy program. ...reports Monday suggest the affected parties have been notified of the [WTO]'s decision to side with the complainants...The WTO ruling is non-binding, meaning Ontario could simply ignore it and not face any monetary punishment. But such a move would likely be met with the implementation of tariffs against any Ontario-made goods in Japan and the EU.

Simon thinks the word "binding" does not tell us much if retaliatory tariffs could be imposed in the event Ontario ignored the ruling. Instead, he says "the key question is how effective the enforcement mechanism is."

I'd agree-it's equivalent to the maxim that "tax administration is tax policy." In international tax there is no doubt that the question is not the substance of standards, rules, or even norms, but rather what countries actually do, and that happens daily through hundreds and maybe thousands of completely opaque diplomatic interactions (competent authority agreements). Adding arbitration to this mix adds yet another layer of administration and enforcement mechanisms and all the attendant problems that go along with them.