Another Awesome Humble Bundle

Recently the Humble Indie Bundle 11 launched, with 4+2 games. Naturally I purchased the bundle and have been enjoying its content, and can recommend purchasing it to others.
For those who do not know, Humble Bundle, the company, is known for putting together bundles of video games and selling them using a pay-what-you-want model. That's right, you decide how much to pay for the games. What's more, you also decide what happens to your money, by sending customizable portions to the game developers, which are typically independent devs, charity, or to Humble Bundle itself. The company can proudly boast that they have raised millions of dollars this way, thanks to the generosity of gamers, and developers. We cannot neglect the generosity of the developers, who are offering their creations to charity just as much as we are offering our money.

Recently Humble Bundle posted something on Google+ about contacting them if we had supported the Red Cross through them. Apparently the Red Cross wanted to do an article or something about gamers for charity. This got me thinking about why Humble Bundle may succeed as a source of funds for charities.
The easiest answer is that people want to take advantage of the pay-what-you-want model, and from that money is provided to the charities. While the model is no-doubt involved, I suspect the most-correct answer is something different. Something that also explains why people will still spend hundreds of dollars when they do not need to.
That easy answer above fits with an assumption that gamers are selfish people (all healthy people are selfish in some way, whether it be for food and drink to satisfy, or warmth to survive). If that were the case then we could not see sales much greater than the minimum possible prices, yet we do. This would suggest that gamers are charitable. I believe that both are true, and that the correct answer lies mostly with this latter point.
I believe the reason Humble Bundle has been so successful as a source of revenue for charities is because of its existence, and not its model. It provides gamers with a mechanism to be charitable, and so we are. Without a mechanism to be charitable, we are not charitable. The model Humble Bundle uses will subtly encourage people to purchase the bundles, as it puts valuation in our control.
Let me also say this. The most passionate and happy people, are typically the most charitable. This makes sense because if someone is happy, they are more willing and interested in sharing that happiness and their passion. Gamers, by being gamers, are passionate, and games are meant to entertain us, and entertainment can lead to happiness.
The gaming population is primed to be charitable, leaving only the mechanism to be charitable to be determined. Humble Bundle, and many other companies provide us with that mechanism.
I think I just talked more than I had to. I'll stop now.