Actually I didn't use the JSON-RPC-PHP class at all. I recreated this from scratch, since it is using the same kind of communication it will ofcourse have some similarities. One of the main differences are that this uses cURL instead of fopen and just has a nicer way of handling errors. Also, I know it's not much, but this one is case sensitive, I personally find getBalance() better practice then getbalance(). If you don't prefer this version, by all means do use the JSON-RPC-PHP verison.
I had no intention of mocking you or saying that your php class was not good, it was just me thinking "why re-invent the wheel" etc. But hey, the incentive is great, and perhaps you'll even develop your script to a stage where it's really awesome!