This looks right to me. Consider.
Arminianism is true.
W1 is a world in which I do sin at 8:15 PM on Mon. Aug. 24, 2009 (henceforth known as time t).
W2 is a world in which I do not sin at time t.
Assuming I made a moral choice at time t, the difference between these worlds is traceable to my free choice. (It's a little more complicated on Molinist Arminianism, but it still holds.) The difference is my free decision.
Calvinism is true.
Same two worlds.
The difference is the result of what God, before the foundation of the world, decreed would happen. I may have wanted to do what I did, but given what God chose to have happen, I either acted on the desire to sin or acted on the desire not to sin.