I believe Marco got at least a couple million dollars from the ~$1B sale of Tumblr (dilution, not clear how much he started with, etc.). That's actually a lot of padding, and means that he can get by for a year or so to try out this free + patronage model. Someone that needs an income, doesn't have that luxury.
I think the patronage model is interesting, and I'm curious how he or other developers will make it work within the confines of the App Store.
This is a guy whose tech podcast I stopped listening to partly because he and some other dweeb wouldn't shut up about their brand new BMWs.
If you work alone and you have a few million dollars of fun money to burn, that changes people's perception of you. Now you're not doing it because you have to. Where's the struggle? Now you're just entertaining yourself.
It's like saying Bill Gates is an "independent charity volunteer." Doesn't quite get the point across.
Topping the charts for a day amounts to tens of thousands of dollars. To most people that's a non-trivial amount of money to toss away to maintain one's sense of morality.