I think that status-code is not like a symbol, because there is some logic, like 2xx are success codes and 5xx are server errors. So, sometimes you need to do some mathematical comparison.
I understand, that you can check first character of string, but programming languages use int values.
For example Java class HttpServletResponseWrapper uses int as argument for setStatus().
C# HttpResponse.StatusCode set/get int value.
PHP has method http_response_code() which accepts int as status code.
So, if implementation of JSON API returns string value (as required by specification), I need to convert it to int value to send response to client.