Re: 3% pay costs for the other 97%
"3% pay costs for the other 97% hardly seems fair."
Why not? That's just how progressive taxation works, which is generally considered the most fair way of doing things. Those with large incomes pay more than those with small. Since a very small number have incomes orders of magnitude higher than most, that small percentage ends up paying the vast majority of fees. The alternative is for everyone to pay the same flat fee, which is unfair on the little people who may well not make enough to afford the fee at all*. And unlike actual taxation where a government could just say tough and come and take it anyway, for an app store that means you've driven away 97% of your developers. Even if those 97% aren't making Google a significant income directly, the fact that they are there is a large part of the reason people use Android phones and the app store at all.
* A combination of the two doesn't make any difference. Any flat fee is too much for those with zero income, while no flat fee can be large enough to compensate for the difference in percentage fees from apps with many orders of magnitude higher income than others.