So you're argument is that an online digital store justifies a higher fee (30% vs 22%) even though it's significantly less expensive for Apple to run a digital store than it is for Best Buy to operate physical retail stores?

If anything, that's just evidence that Apple is grossing abusing its market position.

If Best Buy doesn't sell the software, they lose money, because A. They already paid the developer for it. B. It takes up space that could be used to sell something else. If Best Buy wants to sell it at a discount, it doesn't affect the developer, they were already paid by Best Buy.

With Apple, its the opposite. If Apple sells something at a discount, the developer suffers (or Apple has to pay the difference in some countries). If it doesn't sell, no one gets any cash. Apple has no incentive to market something and/or move inventory. Apple has only the incentive to market things that you spend money on vs. Best Buy that has to take a risk on something by spending money to buy it from the publisher first.

We receive vendor allowances for various programs, primarily volume incentives and reimbursements for specific costs such as markdowns, margin protection, advertising and sales incentives. Vendor allowances provided as a reimbursement of specific, incremental and identifiable costs incurred to promote a vendor’s products are included as an expense reduction when the cost is incurred. All other vendor allowances, including vendor allowances received in excess of our cost to promote a vendor’s product, are initially deferred and recorded as a reduction of merchandise inventories.

If Apple lists an app on the app store and it does not sell, how much money does Apple lose?

As much as Best Buy did, since they required vendors to reimburse them for markdowns and unsold investory.

We receive vendor allowances for various programs, primarily volume incentives and reimbursements for specific costs such as markdowns, margin protection, advertising and sales incentives. Vendor allowances provided as a reimbursement of specific, incremental and identifiable costs incurred to promote a vendor’s products are included as an expense reduction when the cost is incurred. All other vendor allowances, including vendor allowances received in excess of our cost to promote a vendor’s product, are initially deferred and recorded as a reduction of merchandise inventories.

Why does Best Buy require vendors to reimburse them for markdowns and unsold inventory? Why doesn't Apple do the same?

Right, but there are at least many competitors to Best Buy all competing for your business, driving down margins. Running physical stores is costly. If Apple allowed competing digital stores, I would expect margins would be less than 30%, and even less than 22%, and the value would end up in consumer and developer's pockets.

Google allows competing stores but this isn't the case.