I don't understand your point. The semantics around type-handling are very clearly defined in the JSON spec: a number is simply a series of digits (plus decimal

I don't understand your point. The semantics around type-handling are very clearly defined in the JSON spec: a number is simply a series of digits (plus decimal point, - sign, etc.). If you choose to interpret that JSON in a language with less than infinite precision, then you need to accept that some data loss can occur. That will happen if you're mushing an XML string into a number type, too.