I don't think they're charging their store fee, because their store cut is 30% (that's the percentage cut Microsoft and Sony take from everything sold on their online stores), whilst the percentage in question is 22%, which is why many assume it is instead the VAT (20%) plus transaction fees (2-3%). If it was the store cut, the percentage would be higher. I assume for different US states different taxes and fees apply, hence the wording on the US side of things, but I don't know how US charity and tax law works.
I think Microsoft and Blizzard are probably forking the costs of the taxes and fees themselves, whilst Sony is not, or they have a registered charity outlet as a side that they can parse things through to cover those things, whilst Sony does not. Either way, not a good look for Sony, especially when your major competitor is doing it. I won't speak of Blizzard because it goes without saying that Blizzard would cover the cost of taxes and fees given it is their charitable initiative in the first place, eg if you're already giving away the proceeds of this purchasable item, you might as well go the whole way.
