Most YAML users don't need to look at the source for a YAML parser. I appreciate elegant simplicity, but I don't think parser complexity is the most important metric by which to judge a data interchange format.

If you use a YAML parser to parse JSON-with-comments, it will accept many inputs that don't correspond to JSON-with-comments, and furthermore is likely to report syntax errors that don't make sense to a user who only knows JSON.

So, this unnecessary parser complexity is a usability issue. You should use a parser for the config language you actually intend to support.