The withdrawn invitation links the uninteresting royal wedding story with something important, and it makes royal wedding enthusiasts more aware of things elsewhere in the world that actually matter, but it doesn’t make much sense as a matter of British policy.
Many other equally abusive or even more wretched governments will have their representatives in attendance, because Britain has diplomatic relations with many governments whose human rights records are no better and some of which are far worse. Even though it goes against the Foreign Office’s own view of what invitations to these events mean, Syria is out because Syria happens to be the cause celebre this week. Call it the CNN-and-tabloids effect. Like everything else about British foreign policy lately, the decision-making here is purely reactive and opportunistic.
Like, er, the Libya mess. The NYT today offered a figure of 30,000 possible civilian deaths so far. How many before the intervention? Obviously, there's no counter-factual and Qaddafi's triumph would have been awful. But sometimes freezing conflicts into drawn-out stalemates is not the most efficient way of preventing civilian deaths, if that is your sole criterion.