Products sold in wallmart can then provide extra external services which walmart gets no cut of. If I buy an air purifier in Walmart, they get a cut on that initial sale. But the purifier company can tell me they sell filters on their website, Walmart gets no cut of that. On mobile, Apple does get a cut on that sale which they did not facilitate.
The difference is Walmart holds so much less power. It would be like if Walmart owned the exclusive ability to delivery packages to 50% of houses in the world, and then no matter what the filter company does, they can't avoid this fee because Walmart holds their huge captive market and is able to extract these fees without adding much if anything to the transaction.
