My head hurts

I was listening to a commercial on the radio as I returned to work this afternoon from my final at Talbot. The spot was for MSN music downloads or something like that. I really was not paying too close of attention. They were offering 5 free downloads if you pay $0.99 for one. The deal seemed interesting so I started to pay attention more. I was sure there would be a catch. Sure the verbal small print first confirmed my suspicion then hurt my head. The limit is that this offer is good only one per customer. That makes sense. The limitation that made me hurt however was the phrase "while supplies last." Tell me if I am missing anything, but how could you run out of a download. What are you going to try to download B.Y.O.B. by System of a Down and have a pop-up tell you that they are all out but that if you like you can have Jessica Simpson's remake of the "These Boots are Made for Walking"?