Indeed, thinking of Marco Arment as an "indie dev" is sort of like thinking of Minecraft as an "indie game." Regardless of roots, at some point, they both crossed a money line. That being said, assuming he is somewhat financially prudent, Arment probably has enough money to just drop into mutual funds and live off the interest, so I guess it says something about his passion as a developer that he's still coding and trying to make an honest buck off of it.

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.