pielak you are right but truth is peppy lives out of this, makes money with this and will try to make as many as he can. That's just good, he works on this project because he knows the better he does the more players the game will get and the more money he is going to earn. I'd rather have that than osu! being a side-project since he is busy with another job/other project, dunno about you.
You are not forced to buy anything from the osu! Amazon Store, if you feel like it's unfair you can buy from regular Amazon. If he gave out a supporter tag equivalent to the amount of money he is getting from your purchase, that would benefit a 3rd party and I think he doesn't give a fuck about that third party, which is fine why would you care about Amazon getting more sales lol.