They also contractually forbid merchants from taking actions that could make the fee more apparent to consumers, which drives up prices for non-credit customers, although there isn't a direct analog for Apple I can think of.
Has this changed over time, though? I often see a lot of brick-and-mortar merchants advertising different prices for cash/debit vs. credit. I probably see it most often at gas stations, but I see it in regular retail stores and restaurants sometimes as well. I moved to a new house earlier this year and even the movers offered a lower price for cash.
[1] https://www.lexology.com/library/detail.aspx?g=c1069ffd-dafb... (hopefully the link works)