But what's the point of rejecting an edit like this, claiming that it changes the sense the post makes? That edit was done to a Showcase of Languages entry, and all it did was to add two snippets whose lengths don't exceed the vote count of the post - it's something the original poster would definitely accept. Why not do such an edit?
While the whole community can edit all posts (or, at least, suggest it), most posts still have a single owner. Editing a post should be used to improve it in obvious ways that do not require the author's consent (fixing spelling mistakes, improving grammar, adding useful information such as a permalink or a leader board snippet), but never in ways that may conflict with the author's intentions.
Furthermore, PPCG isn't really a Q&A site. It makes more sense to improve an answer to a question than to change (or add to) the code in a competition. As a rule of thumb, if your intention is to add, remove or change the code in an answer, don't. Leaving a comment (golfing suggestion, additional snippet, etc.) that the author might edit into his post is perfectly fine and usually welcomed though.
The only exception to the above are community wiki posts. While usually (and mistakenly, in my opinion) used as a rep waiver, their intended use case is to create questions or answers where everyone can "chip in". These posts essentially belong to the whole community rather than a single member of it.
It's the same as edits that golf other people's code, other than the challenge's objective type. We expect that the code that forms the answer to a challenge should be written solely by the original poster of the answer, with the possible exception of community wiki posts.
It's worth pointing out that the answers above are of historical interest only. The language showcase has been changed to community wiki status (so that posts don't have an owner and the barrier to editing is lower); it's likely that this sort of edit would be accepted now (possibly even without approval).