They are just making sure that elders do not attach to the dictionary definition of "addiction". If you are on xanax, you are technically using an addictive drug. If you had just smoked your first pot cigarette, you are not an addict yet, but you are on your way there. Xanax could be seen the same way. In fact, my doctor told me once that I could just drink instead of taking Xanax, the effect would be the same but he said Xanax is better because it would not damage your liver in the long run. When I wanted to cut Xanax out, i was told I needed to do it in stages to avoid withdrawal.
if a brother is on Xanax, he should not be tried in a JC. That is what that loophole is. However, some people may take this medication under doctor supervision but many times these celebrities have bought the doctors to push the limits. Basically you are getting high under doctor supervision, in excess of the amounts recommended for your condition or at least without exploring other alternatives. The Watchtower isn't going to taint their hands any further than they already have, by providing doctrine that discourages people from taking medication that would prevent, for example, suicidal tendencies.
In my view, and based on the obvious outcome, it is clear, like many other celebrities, were getting doctors to prescribe them this type of medication to get high, not to get treated. And therefore the loophole should not apply.