I have very little understanding of JSON, so why would this happen?
JavaScript is using double as a number. There's no such thing like integer or floating point numbers per se, only so called Number.
Described issue is not problem of a JSON but engine which parsed it and language which stands behind the parser. Any config format will eventually have same result and same issue.
So forcing programmer to parse every single piece of data for sake of "it's his responsibility" is not a case here.
I also disagree this is in any way programmer responsibility to create standardized way of creating parser for everything. This format gives you nothing but indentation so you are forced to create documentation for everything field, what type it's and what kind of values it takes. Lots of extra work for nothing when you have any other format.
That's one more thing you can afford to not understand and still be productive.