Edit (added): Thinking more on this, I wonder if the Humble Bundle folks actually get the tax benefit of the donations.
I think you nailed an important part there. Clearly customers can't write anything off (since they aren't giving money to a 501(c)(3) directly, but obviously someone is. I can't remember what the default split was exactly, but if you figure it was 5% tip, 5% eff 5% child's play,the operator would be seeing more like 8.33% by default when the tax advantage came into play. If you assume a lot of people went mostly or totally for charity (especially for the large amounts) their margins would actually be rising.
I think you nailed an important part there. Clearly customers can't write anything off (since they aren't giving money to a 501(c)(3) directly, but obviously someone is. I can't remember what the default split was exactly, but if you figure it was 5% tip, 5% eff 5% child's play,the operator would be seeing more like 8.33% by default when the tax advantage came into play. If you assume a lot of people went mostly or totally for charity (especially for the large amounts) their margins would actually be rising.