Choice is not censorship. As far as I can tell, Wikimedia is considering to add the option for users to block images that have been flagged as potentially offensive. Since Wikipedia covers many aspects of humanity, some of them scary, it makes sense to enable users to filter some of the more graphic aspects of this. Remember, the articles themselves will not be blocked. I think this would make Wikipedia more useful for kids that might not have the tools to deal with looking straight into another person's guts just because their reading up on surgery.
Many other sites, such as DeviantArt, block nudity by default, and to view it you must register an account and turn the filter off. Even though this is opt-out and a bit extreme, calling the practice censorship is ridiculous.