Anyone who thinks a 30% cut is excessive has apparently never sold anything through an actual store before. If you can get something into a bricks and mortar store and 30% of the retail price is actually going to you, you'd be extremely lucky.
I'm really not sure how the analogy is relevant. You set a starting cost, then a brick and mortar store ups the price in order to pay for the costs of running business and to gain a profit. Microsoft on the other hand has a fee for potential customers to enter the store -- the price of a copy of a Windows OS -- and has relatively small costs per each app added to the store, since the space required for one app on their server doesn't really amount to much. Microsoft is closer to a wholesaler w/ a membership fee and very little marginal cost.