Considering Google takes all of the risk, and creates an environment where it's much easier to create value than on your own, I think it's more than fair.
Are the reduced risk and added infrastructure really worth Google's 90% cut?
That's the important comparison - it's quite possible for you to keep 100% of the value you create, but only create $60-70K/year of value. Several of my college friends (not in the valley) are in that position.