Yeah, that's the thing - in some jurisdictions trading alternate 'digital' currency with any value at all can still be considered 'gambling', regardless of who owns the currency (you or S-E,) what its relative dollar value is, and so on, and so forth.
Even in the US, whether or not your fake internet MMO items have value that could be considered something you can gamble on is a nebulous legal issue, because once players start trying to collect it and cash it in for digital goods it could be considered to have some form of money value attributed to it. This tends to be a matter of intentfulness - even paying 50 MGP to 'play the typhon game' looks a lot different than 'betting 500 MGP on a virtual race' in court.
