Interesting experient. I would say that for people who are not addictd to gambling, the reason they are willing to put money in a slot machine (or any other gambling where they know they are unlikely to win) is that although the chance of winning is remote, the risk is low (you aren't gambling a huge amount per play) and there is a small chance that you could win far more than you are risking.

There is also the "thrill" of playing a game that factors in. Myself, when I go to Las Vegas, I determine before I go how much I am willing to risk gambling, and I stick to that amount. I know the liklihood of winning is very small, but it's still "fun" to try.