Another simple question... If you don't need money, why you would "only" give 25% to charity? I'd give it all to charity like David Gilmour did with his insane auction. Of course, nobody asks you to donate anything, but just from the logic perspective it doesn't make sense. "I don't need the money, but I'll keep 75%, thank you very much".
I would suggest that you take this thing by the wrong side.
This is not a question of "needing money" but simply to "deal with money".
Myself needed to reflect on it because I found it strange the first time I read about this "25% charity donation".
But this is Mark deciding to sell a part from his collection for whatever reason.
I would feel wrong to question the fact he's keeping the money to him.
Basic fact it wasn't meant to be a charity auction and nobody would have dared to question this.
But still, Mark had the generosity to give a percentage to charity.
And then the question arise : only 25 % why not 100% after all, he does not need that money?
Utterly wrong questionning for my part even if I did not avoid from it at first.