What would cause the hypothesized event to occur is skipped over. Normally this is fine, but the workings of the decision-making process are themselves in question, the hidden assumptions that are being made about them are of relevance. That is what caused my confusion over the Newcomb's Paradox / Voting question — which could only be understood by making explicit the process by which the hypothetical decision was being made.
Political questions are similar — when one says "If the UK were to reject the new EU Treaty then ...", one is skipping over the question of how the rejection is to be reached. I tend to flippantly express opinions as to policy in the form "If I were Supreme Führer, ..." which is a way of alerting listeners to the fact that realistic mechanisms are being ignored for the purposes of discussion.
As with Newcomb's paradox, but scaled up to the polity, when the mechanism of political decision-making itself is part of the question, hypotheticals which brush aside the mechanics are pretty much meaningless. "If we had PR / yearly parliaments / a 'Formalist State' — the specific changes that would make such changes possible would be as significant for the consequences as would the hypothesized changes themselves, so it is a bad idea to ignore them.
Mencius' "magic ring" is the equivalent for political structure of my "if I were Führer" for particular policies: whatever realistic means are put forward to achieve a similar political structure, those means will have their own side-effects on the end result.