I didn't say they were gifts, just that gifts and earnings are treated separately. If they are classified as gifts (despite what someone wrote in a legally non-binding FAQ), then there's your answer.
However, you did not technically "compete" or "enter a contest" to get those credits, so they could probably be construed as gifts. WGT is not obligated to pay them to you based on a specific tournament that you entered, thus it's not considered a contest and contest rules do not apply. Just a guess, I'm no tax pro.
What amazes me is the sheer number of people complaining about being handed something for nothing. There's no conspiracy to hose internationals here, that would be a bad business model.
=/