If you go on IRC, the people make it very clear that they're not doing this for donations, but for the "fun" of hacking. It's like picking a lock. They want to see if they can.
They say that, while they appreciate the tips (for pizza), it's more about the joy of exploration for them. The tips are secondary.
For those that are asking for iPod touches, right now they're having to relay their ideas to (less skilled) users who happen to own them. This is much slower than if they had an iPod touch themselves. But even though they don't, they still try to help.
It's not about money, it's about practicality.