This practice is common in digital marketplaces. For instance, Amazon doesn't allow Marketplace Sellers (people who aren't Amazon but sell goods on Amazon.com) to:

- link to a non-Amazon webpage

- provide buyers with a phone number or email address to reach them at

- or any other thing that could funnel sales outside of Amazon

Not quite sure what you mean by hardware folks? Any physical good sold in an app from the Apple App Store has to be processed by the vendors payment processor not by Apple.