I guess maintaining compatibility with JavaScript is more important than minor space optimizations. Also, if you really care about such things, you shouldn't use JSON in the first place (see Protocol Buffers etc.)
I not advocating for changing the JSON spec. I'm saying, as a human-readable data format, it could be more compact. Perhaps this observation can be useful to those who are designing a new language.
If this format is intended to be primarily human-readable, why should compactness be so crucial? Looking at your example, I personally think that commas increase readability by visually separating individual elements (at the expense of space they take).
This HN post is a discussion about data expressions leaner than JSON. I believe the points I've made contributes to it and I've never said such compactness is more preferable. It's merely an observation.
