Ummm... did you even read what they wrote? "Ebay is one of many outlets that we use to sell these parts online." See that? One of many. And Ebay does have policies on what you can and cannot sell on their website.But if you want to sell your products through a different channel than Ebay, YOU are allowed to do that. Any apps on IOS must be both approved and sold through Apple. I have an idea, let's encourage Ebay to first review and approve your diesel parts to be sold on their network before you are allowed to sell on Ebay ... how would you like them Apples.
Ebay doesn't forbid you from selling products through a different channel, and neither does Apple. Last time I checked, Spotify is on Android too. Apple doesn't forbid developers from making an Android version, Windows version, Blackberry, Firefox OS, <your preferred OS here> version either. That's all up to Spotify. Spotify is basically saying, "Apple should do all the hard work spending years and billions of dollars setting up a successful app ecosystem and then let us use that ecosystem for free."