I understand the distinction, but it's imperfect. See below examples where Apple does not presently charge a 30% fee. There is a big grey area between digital items and physical items.
I can buy a Spotify gift card in the Amazon iOS app, which just emails me a code a short while later; no physical card even. If it's just a code that exists in email, isn't that a digital item?
Services, whether it be a driver (Uber/Lyft), a cleaner (Handy/Tidy), a food delivery (Grubhub/UberEats), a dog walker (Rover/Wag), furniture assembly (TaskRabbit), shipping (UPS, FedEx, Stamps.Com), can all be purchased in app. I'd argue all of these are closer to digital items than they are to physical items. It's a service transacted over the internet, isn't that digital?
At the same time, I understand the conundrum for Apple. If they didn't charge a fee for digital IAPs, then all paid apps would become free with a paid IAP and Apple would get nothing. I don't think this problem is fixable.
I think Apple has to decide: do they want to monetize a platform, or do they want to sell on their platform. They can't do both without running into serious antitrust issues. I think Apple would be more interested in trying to grow their services. Indeed, they're apparently going to announce a movies/tv service later this month. For this reason, I think Apple should just drop the 30% fee entirely, offer ApplePay as a convenient way to process payments but also allow other payment processing APIs to plug into their system (PayPal, Visa, Mastercard, AmEx, Shopify, Square, etc.). Basically, give up monetizing the platform.