In theory, it makes sense that less than 6 characters modifications that turn a code example into a compilable one should be allowed, at least to me. It can be annoying when you try to answer a question, and the SSCCE provided doesn't compile because of some stupid mistake that could be easily fixed (typo, wrong indentation in case of Python, etc.).
As @animuson pointed out, this only applies to users with less than 2000 reputation. But still, I think if those users find out an error in a SSCCE and want to spend a few seconds to make it easier for others to answer the question, they should be able to do so. Going through posting a comment and waiting for the OP to make the change (or someone else with more than 2000 reputation) seems like an incorrect use of the comments. Once the code modification is done, you would end up with 2 or 3 comments that are irrelevant now that the problem has been fixed.
However, I wonder how often this case happens. If it's once every month, then I guess nothing should be done about it. But if this situation comes up 2-3 times a day, then maybe an easy solution could be investigated? Maybe small modifications made to code blocks only could automatically be submitted for review instead of being refused automatically by the system? Specifying a comment in this situation would then be mandatory, just to make sure the user editing the question can specify to the reviewer why such a change is being submitted.