inconsistent RPC fee return types

I found this in the rpc documentation:

"fee":{
    title":"Amount in mutez",
    "oneOf":[
       {
        "type":"integer",
        "minimum":-2147483648,
        "maximum":2147483647
       },
       {
        "type":"string"
       }
    ]
},

is there a special reason to return this value in one of 2 possible formats? because if not, the api would be a lot easier to consume in statically typed languages if it would only be integer, or only be string

Edit: also applies to transaction -> amount and origination -> balance